Histology

Question 1

Name the three layers of the skin

Answer 1

1. Epidermis

Keratinised stratified squamous epithelium

Keratinocytes = true epithelial cells

1. Dermis

Dense irregular connective tissue

1. Hypodermis

Addipose tissue

Question 2

Explain how you would distinguish between thick and thin skin?

Answer 2

Thick skin

• lacks hair follicles
• nasal planum, footpads
• has both stratum lucidum and stratum corneum layers

Thin skin

• most frequent and is usually haired
• no strtum lucidum

Question 3

Identify all five layers of the epidermis ?

Answer 3

1. Stratum basale
2. Stratum spinosum
3. Stratum granulosum
4. Stratum lucidum
5. Stratum corneum

Question 4

Identify and describe the Stratum basale ?

Answer 4

Stratum basale

• single row of cells sitting on a basement membrane
• stem cells undergo mitosis

Question 5

Identify and describe the Stratum Spinosum ?

Answer 5

Spinosum

• cells have spines projecting (cytoplasmic extension) and attach to each other via desomeres

Question 6

Describe and identify the Stratum Granulosum ?

Answer 6

Stratum Granulosum

• keratin accumulates in cells
• contains keratohyaline granules - start to bind keratin together and Lamella granules - water proofing

Question 7

Describe and identify the Stratum Lucidum ?

Answer 7

Stratum Lucidum

• contains a protein which has a different staining affinity
• above granulosa layer, only in thick skin
• flattened dead cells of poor staining quality

Question 8

Describe and identify the stratum corneum ?

Answer 8

Stratum Corneum

• consisting of dead accumulated, anucleated squamous cells containg keratin
• layers depend upon the site of tissue

Question 9

Explain what the epidermis is composed of and where it is located ?

Answer 9

Epidermis

• the most superficial layer of squamous epithelium
• accompanied by other cell types for pigmentation, sensory perception and immune function
• derived from ectoderm layer of the trilaminar germ disc.

Keratinocytes = true epithelial cells

Question 10

Describe Langerhans cells their location, function and structure ?

Answer 10

Langerhans cells

• found at the level of the stratum spinosum
• involved in immune function
• function as antigen presenting cells and may stimulate T cell responses in various allergic or inflammatory responses
• well characterised in humans and rodents

Question 11

Describe what melanocytes do, their location and function ?

Answer 11

Melanocytes

• reside in the stratum basale layer of the epidermis
• originate in the neural crest of the ectoderm
• pigments may travel from basal layers to upper layers through specific processes - eventually phagocytosed by keratinocytes

They function to absorb and scatter UV radiation thus decreasing mutagenic effects

Question 12

Describe the dermis, its location, composition and two layers ?

Answer 12

Dermis

• Located beneath the epidermis
• able to withstand certain mechanical stressers as it is both flexible and elastic
• thick layer of connective tissue
• dense irregular connective tissue
• contains blood vessels, lymphatics and inflammatory cells (histamine and heparin).
• develops from mesoderm of the trilaminar disc

Papillary layer = fine collagen fibres richly supplied with cappillaries

Reticular layer = Highly thick collagen bundles

Question 13

Describe the location and composition of the Hypodermis ?

Answer 13

Hypodermis

The majority of the tissue is composed of adipose

but there are also, sweat glands, hair follicles, large vessels, nerves and lymphatics, skeletal muscle, mammary glands etc

Question 14

Sebacious glands what do they produce, where are they located and what are they derived from ?

Answer 14

Sebacious glands (holocrine)

• derived from the epidermis
• solidly packed cells with a foamy appearance
• produce sebum an oily product that waterproofs or softens the hair
• glands empty into upper regions of hair follicles
• all the contents of the cell are lost to the cells surface

Question 15

Describe hair follicles origin, and accompanying cells.

Answer 15

Hair follicles

Specialised down growth of the epidermis that extends deeply into the dermis and hypodermis

• hair growth originates at the bulb
• melanocytes provide pigment to matrix cells which are eventually formed into hard keratine
• arrector pilli muscles = smooth muscle attached to root sheath allow hair to become erect when cold

Question 16

Identify the dermal root sheath, external root sheath, internal root sheath, hair and cuticle in a hair follicle ?

Answer 16

Question 17

Describe the three stages of hair growth Anagen, Catagen and Telogen ?

Answer 17

Anagen

• Growth phase
• Dermal papilla (uppermost layer of the dermis) reattaches to a new hair follicle
• older hair pushed out by the growth of a new hair follicle

Catagen

• The dermal papilla detaches and rests, while the hair shaft is freed from the blood suplly and pushed upward

Telogen

• Dermal papilla reattaches to new hair follicle (Dose not grow)

Question 18

Describe Apocrine glands and what they produce ?

Answer 18

Apocrine glands

• located throughout the skin of most domesticated animals
• empties into upper part of hair follicle
• simple cuboidal epithelium, coiled glands
• not true sweat glands produce = viscous fluid, sexual attraction, communication, territorial marking
• excretes a small portion of the cell contents and secretion

Question 19

Describe Merocrine sweat glands and what they produce ?

Answer 19

Merocrine sweat glands ?

• simple cuboidal or columnar epithelium
• produce aqueous sweat for thermoregulation
• open directly onto the surface of the skin
• only secretion is lost to the cell surface

Found

• footpad of dog and cat (picture attached)
• frog of horse
• planum rostrale and carpal glands of pig
• nasolabial region in cattle

Question 20

Describe the blood supply to the skin ?

Answer 20

Question 21

Describe the formation of hooves, horns and claws ?

Answer 21

Hooves, horns and claws

Same structures as thick skin

They differ through the shape of the papillae / lamellae that extend from the dermis

Flat papillae = form flattish thick skin

Shaped papillae = form keratinised columns hooves, horns and claws

The hoof/ horn is held to underlying tissues through laminae

Question 22

Identify the three layers of skin in a pigs ear, what features make this a thin skin classification ?

Answer 22

Pig ear thin skin

Thin skin as it lacks a stratum lucidum layer and contains many hair follicles

• blue = hypodermis
• pink = dermis
• purple = epidermis

Question 23

Identify the four layers of the epidermis in the thin skin of a pigs ear ?

Answer 23

Epidermis

yellow = stratum basale

blue = stratum spinosum

green = stratum lucidum

orange = stratum corneum

Question 24

Identify the five skin layers in a dogs paw pad, what characteristics make this thick skin ?

Answer 24

Dog paw pad

This is thick skin as it has an incredable thick keratinous layer composed of stratum lucidum and stratum corneum (usually lacks hair follicles)

yellow = stratum basale

blue = stratum spinosum

green = stratum granulosum

purple = stratum lucidum

orange = starum corneum

Question 25

Describe the nasal cavity regions and what structures maintain its shape ?

Answer 25

Nasal cavity The structure is maintained by bone and cartilage of the nasal bones (maxillary, incisive, ethmoid and frontal) with the cartilage of the chonca. The left and right side is divided by the nasal septums. Three regions of the nasal cavity * Rostral (Cutaneous) - comprised of stratified cuboidal to non - ciliated pseudostratified columnar * Respiratory (caudal to thirds) ciliated pseudostratified columnar epithelium * Olfactory (dorsocaudal) ciliated pseudostratified columnar epithelium with olfactory epithelium

Question 26

Describe the specialisation of the ethmoid choncae within the respiratory system ?

Answer 26

The ethmoid choncae contains specialised olfactory epithelium * Respiratory epithelium specialised for olfaction * located near the ethmoid and the roof of the nasal cavity * Bowmans capsule = moistens olfactory mucosa * Olfactory cells long cilia contain receptors * Sustantacular cells = supportive cells of olfactory epithelium * Basal cells = stem cells

Question 27

Describe the histology and identifying features of the trachea ?

Answer 27

Trachea * C rings of hyaline cartilage * pseudostratified columnar epithelium * Trachealis muscle contracts during coughing to increase intrathoracic pressure * large submuscosa contains specialised glands (seromucous glands) * goblet cells = secrete mucous * Cilia = moves mucous cranially * laminar prpria lie below the epithelium and is greatly vascularised.

Question 28

Describe the distinctive histological features of the Bronchi?

Answer 28

Bronchi (primary to secondary) * irregular plates of cartilage in wall * smooth muscle which surrounds the laminar propar * depper the cartilage plates become less regular * the number of glands decrease with increasing depth into the long

Question 29

Describe the histological features of the Bronchioles ?

Answer 29

Bronchioles * no cartilage in walls * deeper at this level the epithelium becomes simple columnar * contains club cells * terminal bronchioles transition to respiratory bronchioles when alveoli begin to appear on the slide.

Question 30

What do club cells do and where are they located ?

Answer 30

Club cells are located within the bronchioles * dome shaped cells with short microvilli * detoxifies cytochrome P450 enzymes which break down air born toxins * act as stem cells to replenish bronchiloar epithelial cells

Question 31

Describe the histological features of the alveolar, and the three cell types ?

Answer 31

Alveoli * honeycomb arrangement * abundant capillaries, supported by collagen and elastin fibres **Type one pneumocytes** * simple squamous cells * thin to allow for diffusion * close opposition to capillaries **Type two pneumocytes** * cuboidal cells * produce surfactant to decrease surface tension * stored in lamella bodies (granules) * can also act as stem cells replacing type one and two pneumocytes **Alveoli Macrophages** * immunity against irritants, microbes and particulate matter via phagocytocis

Question 32

Describe the three layers of the heart wall ?

Answer 32

Heart wall * Endocardium simple squamous and dense irregular connective tissue * Myocardium cardiac muscle - striated, single centered nucleus, intercalated disks, branching under involuntary nervous control + contains perkinje fibres * Epicardium (visceral pericardium) ​squamous epithelium loose connective tissue and elastic fibres containing the blood supply and nerves which innervate the heart

Question 33

Identify the layers of a artery ?

Answer 33

Tunica intima endothelium - simple squamous lines the entire vascular system subendothelial layer internal elastic lamina Tunica media smooth muscle layer external elastic laminar Tunica adventitia contains vaso vasorum

Question 34

What is the vaso vasorum and where is it located ?

Answer 34

Vaso vasorum * located in the Tunica adventitia * network of small blood vessels which supply oxygen and nutrition to large blood vessels.

Question 35

What are purkinje fibres, and where are they located ?

Answer 35

Purkinje fibres * modified myocytes * observed between the endocardium and myocardium of the heart (also in myocardium) * transmit and distribute action potentials from the atrioventricular node

Question 36

Describe the dfining histological features of an elastic artery ?

Answer 36

Type one, Elastic artery * The largest arteries including the aorta, common carotid * Tunica intima is thicker - than in other types of arteries (contains subendothelial layer) * Tunica media 10-40 layers fenestrated layers of elastin * Tunica adventitia contains vas vasorum.

Question 37

Define the histological features of a muscular artery ?

Answer 37

Type two Muscular artery * Main distributing branches of the arterial tree eg radial, femoral, coronary artery * Tunica intima - very thin * obvious internal elastic lamina * Tunica media - contains alot of smooth muscle and less elastic fibres * obvious external elastic laminar * Tunica adventitia - variable thickness contains vaso vasorum

Question 38

Define an arteriole through histological features ?

Answer 38

Arteriole * similar histologically as a muscular artery but the small size makes the various layers difficult to discern. * act as sphincters to regulate blood flow to various regions of the body * tunica media only 1-2 layers of smooth muscle * elastic laminae may be absent * tunica adventitia is thin

Question 39

Define the histolical features of a capillaries?

Answer 39

Capillaries * Tunica intima only * endothelial cell enclosed by a basement membrane * lacks tunica media and tunica adventitia * slow blood flow * huge cross sectional surface area * caontain periocytes - contractive cell

Question 40

Describe the three types of capillaries ?

Answer 40

Question 41

Identify the histological features of a vein and how this compares to an artery.

Answer 41

Vein * returns blood to the heart * Tunica intima - contains endothelium and endothelial layer (connective tissue + basement membrane) * Tunica media - smooth muscle much thinner than in an artery * Tunica adventitia - layer of connective tissue containng the vaso vasorum in larger veins * \> 2mm veins contain valves *

Question 42

Describe the how various histological features varie as veins become closer to the heart ?

Answer 42

Variations * thickness of wall * pressence or absence of valves * amount of elastin and smooth muscle

Question 43

Identify the structures (7) ? and tissue ?

Answer 43

Lymph node * afferent lymphatic vessels - entering the lymph node through the capsule * efferent lymphatic vessels - receive lymph from the medullary sinus eventually rejoining the lymphatic system * Subcapsular sinus - the space that encircles the lymph node beneath the capsule into which lymph from the afferent vessels drain * Trabecule - extensions of the outer capsule projecting into the the substance of the lymph node * lymphoid follicles * medullary sinuses - located in the central region they receive lymph from the subscapular and cortical sinusesand converge on the hilum of the node * hilum

Question 44

What is a periocyte ?

Answer 44

Periocyte Periocytes surround the endothelium of capillaries. They are contractile and regulate blood flow through the capillarie beds.

Question 45

Identify the two layers of a lymphoid follicle ?

Answer 45

Lymphiod follicle * Mantle zone - outer layer * The darker staining periphery of the lymphoid follicle where there are numerous T - lymphocytes (cell mediated immunity) * Germinal centre - inner layer * The pale staining centre of the lymphoid follicle where B lymphocytes are stimulated to proliferate by contact with an antigen. (Humeral immune response produce antibodies.

Question 46

Identify this organ and all its histological features ?

Answer 46

The spleen Is a large lymphiod organ that receives a rich blood supply. It provides a region where the blood can come into contact with lymphocytes - similar to the lymph nodes for lymph. * Capsule - a thin fibroelastic coat surrounding the spleen * Trabeculae - extension of outer capsule projecting into the substance of the spleen * Red pulp - forms the bulk of splenic tissue filled with erythrocytes + rich in macrophages * White pulp - pale staining lymphoid aggregates simlar to follicle in lymph node Two types * germinal layer - B lymphocytes * mantle layer - T lymphocytes

Question 47

Identify this tissue and its distinctive histological features ?

Answer 47

Tissue = muco-cutaneous junction Orange = muco-cutaneous junction yellow = orbicularis oris (skeletal muscle) green = hair follicle Blue = keratinised stratified squamous epithelium purple = non keratinised stratified squamous epithelium and seromucous salivary gland.

Question 48

Describe the muco-cutaneous junction, and where is this found ?

Answer 48

Muco-cutaneous junction Junction between the integument and the digestive system * found lips, nose, eyes and nose * in ruminants unlike other species the oral cavity is lined by keratinised stratified squamous epithelium - due to the large amounts of roughage in their diet

Question 49

Identify this tissue, and its defining histological features ?

Answer 49

tongue It is a muscular organ covered by a mucosa and can move in all directions. * dorsal thick keratinised stratified squamous epithelium * Ventral thin keratinised stratified squamous epithelium * intrinsic muscle fasicles run in all different directions. Four types of lingual papillae * Filiform - mechanical * Fungiform * Foliate * Circumvallate

Question 50

Describe structure, location and function of Filiform papillae ?

Answer 50

Type 1 = Filiform papillae Covering dorsal surface of the toungue most common type * purly mechanical and protective * assist with prehension and grooming * move and shape food bolus for swallowing

Question 51

Describe the structure, function and location of fungiform papillae ?

Answer 51

Type 2 Gustatory = Fungiform papillae * mushroom shaped * rise above the surface of the tongue * scattered amongst the filiform papillae on the dorasal surface of the tongue. * non-keratinised stratified epithelium

Question 52

Describe the structure, location and function of Foliate papillae ?

Answer 52

Type 2 Gustatory Foliate papillae * These are leaf shaped * They are located around the sides of the tongue (parallel folds) * absent in ruminants, no taste bud contained within in the cat

Question 53

Identify the structure, location and function of the Circumvallate papillae in the toungue ?

Answer 53

Type two gustatory Circumvallate papillae * surrounded by a mote * largest type of papillae * 3-6 rostral to the root of the tongue * taste buds located in the wall of the papillae * contains the majority of the taste buds

Question 54

Provide the general structure of a tooth ?

Answer 54

Tooth Outerlayer enamel * produced by ameloblasts (96% mineral hydroxyapatite crystals + 1% proteins amelogenins enamelins) Inner layer dentine * avascular, acellular connective tissue - type one collagen * produced by odontoblasts external to the hard dentine * surrounds pulp cavity of the tooth * odontoblasts Below the gum Cementum * cementoblasts * covers the root dentine * similar to bone Periodontal ligament * anchors the tooth to the alveolar bone and absorbs shock

Question 55

Describe the difference between a Brachydont and Hypsodont tooth ?

Answer 55

Brachydont * short * stop growing post eruption * carnivore, human * low crown * narrow canal Hypsodont * long teeth * grow for a portion or throughout the entire life of the animal * high crown * horses, cheek ruminant

Question 56

Describe the development of the teeth ?

Answer 56

Tooth development Enamel can not be repaired but dentin is repairable Ameloblasts * produce enamial * lie external to the enamel * degenerate when tooth erupts, so repair to damaged enamel later in life is impossible Odontoblasts * are external to the hard dentine * have long slender cytoplasmic processes that penetrate the width of the dentin and run in canals (tubules) * these processes are embedded in the secreted matrix Cementoblasts * cementocytes live with in the lucunae within the lower root * cementum is laid down through out life * collagen fibres laid down with in the cementum which eventually forms the peridontal ligamnet.

Question 57

Describe the location of the four major salivary glands ?

Answer 57

Question 58

Describe a serous secretion and where it is produced ?

Answer 58

Serous secretion from a salivary gland * protein and water * adjust PH, aid taste and moisten dry food stuffs * Parotid gland mostly produces a serous secretion Note - secretion exits through the intercalated duct then the striated duct.

Question 59

Moucous secretion where is it produced and what is its function?

Answer 59

Moucous secretion second type of salivary secretion * slippery secretion * aid in bolus formation and lubrication * The buccal salivary gland mostly produces a mucous secretion

Question 60

What is a mixed salivary gland, identify the two types of acini below ?

Answer 60

A mixed salivary gland * identify serous acinus and mucous acinus * produce bothe a serous saliva, and a mucous saliva * sublingual and mandibular gland

Question 61

Describe the salivary duct system ?

Answer 61

Salivary duct system * acinar cells produce the secretion * open into intercalated duct - simple cuboidal * Interlobular duct - simple cuboidal * Large, terminal ducts - striated columnar epithelium

Question 62

Describe the endocrine system ?

Answer 62

Endocrine system * it is ductless * secretory products are known as hormones and released into the blood circulation * high affinity for specific receptors * negative feed-back loops

Question 63

Describe the structure of the pituitary gland ?

Answer 63

Structure of the pituitary gland * Derived from the ectoderm * Pars distilis is the anterior pituitary no connection to the hypothalamus * Pars nervosa posterior pituitary contains the axons nerve fibres from the hypothalamus * Pars intermedia is a simple columnar or pseudostratified columnar epithelium between the pars distilis and pars nervosa * Pars Tuberalis surrounds the infundibulum stalk

Question 64

Describe how the pituiatry gland is derived ?

Answer 64

Pituitary gland * The pituitary gland is derived from ectoderm * The pars distilus (ventral) develops from oral ectoderm by an upgrowth of the diverticulum from the root of the oral cavity * **Rathke's pouch** * The pars nervosa develops by a downgrowth of a part of the dicephelon that eventully forms the floor of the third ventricle

Question 65

Describe the cell types of the Pars distalis ?

Answer 65

Pars distalis anterior pituitary Three distinct cell types **Acidophils** * acidophilic secretory cells * somatotrophs, lactotrophs **Basophils** * basophilic secretory cells * TSH Thyrotrops, Gonadotrophs FSH, LH **Chromophobes** * between acidophils and basophils * poor staining * either old cells / post secretory or stem cells

Question 66

Describe the histology of the the pars intermedia ?

Answer 66

Pars intermedia * Inbetween the anterior and posterior pituitary galnd * simple columnar or pseudostratified columnar epithelium * melanotrophs most common cell type alph melanocyte stimulating hormone *

Question 67

Describe the histolical features of the pars Tuberalis ?

Answer 67

Pars tuberalis * Composed of cell clusters that form a folded tissue with small cyst * traversed by the hypophyseal venules (blood vessels) * Paraenchymal cells have melatonin receptors and are believed to be involved in seasonal regulation of the reproductive cycle in animals.

Question 68

Describe the histology of the pineal gland ?

Answer 68

Pineal gland * flattened cone shaped organ * derived from ectoderm * contain pinalocytes and astrocytes * visual light pinalocytes release serotonin * in the dark serontonin is converted to melotonin

Question 69

Describe the histology of the pars nervosa ?

Answer 69

Pars Nervosa posterior pituitary * Contains axons from the hypothalamus - no nerve cell bodies * **Herring bodies** - dilations of nerve cell fibres * Pituicytes - are glial cells that store and release neurohypophysial hormones * hormones are peptieds released from the hypothalamus bound to carrier proteins and stored in axon terminals * oxytocin, antidiuretic hormone (ADH)

Question 70

Describe the histology and structure of the thyroid gland ?

Answer 70

Thyroid gland * derived from endoderm * Bi-lobed structure containing numerous follicles with cuboidal to simple columnar epithelium * lumen contains "colloid" * thyroid hormones T3 and T4 controls metabolism **C cells (parafollicular cells** * located between the follicles * derived from neural crest cells * produce calcitonin for bone reabsorption * lowers calcium and phosphate levels within the blood

Question 71

Describe the histology and structure of the parathyroid gland ?

Answer 71

Parathyroid gland * derived from endoderm * consist of cell clusters * **Chief cells -** small cuboidal cells with pale cytoplasm secrete PTH * **Oxyphil cells -** esoinophilic cells (stain red) unknown function maby aged chief cells Parathyroid hormone - bone reabsorption and excretion of Ca2+ activates vitamin D

Question 72

Describe the adrenal glands structure ?

Answer 72

Structure adrenal glands Located above the kidney Composed of two endocrine components Cortex * derived from intermediate mesoderm * zona glomerulosa (outer thin) * Zona Fasciculata (middle * Zona reticularis (inner) Medulla * modified sympathetic neurons * derived from neural crest ectoderm * Chromaffin cells and storage granules

Question 73

Describe the layers of the adrenal cortex in detail ?

Answer 73

Outer layer adrenal cortex composed of three layers **Zona glomerulosa** * outer layer, thin * secretes aldosterone reabsord water **Zona Fasciculata** * 70% of cortex * large cells with lipid inclusions * secretes glucocorticoids (cortisol) **Zona reticularis** * small eosinophil cells (red) * secrte weak androgen characteristics

Question 74

Describe the histology of the adrenal gland medulla?

Answer 74

Adrenal gland medulla - inside * modified sympathetic neurons * derive from neural crest ectoderm * Chromaffin cells organised into nest and cords, with a rich vascular network * Storage granules - contain catecholomines (epinephrine, noreepinephrine)

Question 75

Describe the four layers of the gut ?

Answer 75

The four layers of the gut Mucosa * epithelium * lamina propria (thin layer of connective tissue) * muscularis mucosa Submucosa * submucosa glands * blood vessel * nerves * connective tissue Muscularis externa * inner circular muscle layer * outer longitudinal muscle layer Serosa * serosa covers an organ * adventitia attaches an organ to the surrounding tissues

Question 76

Describe the mucosa of the oesophagus ?

Answer 76

Mucosa oesophagus epithelium = * stratified squamous epithelium * may be keratinised in ruminants and horses * functions to protect underlying structures Lamina Propria * dense irregular connective tissue Muscularis mucosa * longitudinal orientated smooth muscle

Question 77

Describe the histological features of the submuscosa, muscularis externa and adventitia within the oseophagus ?

Answer 77

Oesophagus submucosa * loose connective tissue * large arteries, veins, lymph vessels and nerves * seromucous glands Muscularis externa * inner circular muscle * outer longitudinal muscle * the amount of skeletal muscle and smooth muscle varies depending on species Adventitia * loose connective tissue * blood vessels, lymph vessels and nerves

Question 78

Describe this organ?

Answer 78

Stomach mucosa * simple columnar epithelium * surface contains goblet cells - mucous producing cells * produces a thick alkaline mucous to protect the mucosa from the acid stomach contents Gastric pits * numerous funnel like depressions within the mucosa * the cells that line the base and neck of these pits are responsible for gastric secretions * parietal cells secrete HCL and intrinsic factor * Chief cells secrete pepsinogen * neck mucous cells secrete mucous to protect against auto digestion Submucosa * loose connective tissue Muscularis externa * three muscle layer - but three layers are rarely visable * oblique * inner circular * outer longitudinal layer Serosa * thin and barely visable submucosa = contains numerus

Question 79

Distinguish between chief cells, neck cells, enteroendocrine cells and parietal cells ?

Answer 79

Distinguish between chief and parietal cells of the stomach Parietal cells * eosinophilic cytoplasm lots of pink * secrete HCL and intrinsic factor which binds vitamin B12 making it readily available for digestion Chief cells * secrete pepsinogen - once unfolded becomes pepsin which acts to break down proteins into polypeptide fragments. Neck cells * mucous secretion to prevent autodigestion Enteroendocrine cells * stain silver *

Question 80

Describe this structure?

Answer 80

Small intestine Three parts which are similar histologically duodenum, jejunum and ileum Mucosa * **Plicae circulares** - folds in the mucosa / submuscosa * intestinal villi - the lamina propia extends into the folds of each villus * Muscularis mucosa has two layers and also extends into the intestinal villi, where the smooth muscle cells form a longitudinal bundle in their core. **Crypts of lieberkuhn** * openings of glands between the villi run through the lamina propria * lined with simple columnar epithelial cells * **Paneth cells** located at the bottom of the crypts secrete an antibacterial components * **enteroendocrine cells** secrete gastrin and secretin (full)

Question 81

How to distinguish the duodenum histologically ?

Answer 81

Duodenum * the duodenum, jujenum and ileum all have the same intestinal mucosa with villi * **Only the duodenum has a submucosa packed with Brunners glands** * submucosa glands * secrete alkaline mucins into the lumen * acts to neutralise acid from the stomach

Question 82

Identify the paneth and goblet cells of the small intestine ?

Answer 82

Identify the paneth and goblet cells of the small intestine ? Paneth cells * located at the bottom of the crypts of lieberkuhn * secrete antimicrobial agents (lysozyme) Goblet cells * located within the endothelium * secrete mucous for protection from chyme acid

Question 83

What is an lacteal ?

Answer 83

Lacteal * A single lymphatic vessel within the lamina propria of the villis * blind terminal end * contraction of smooth muscle in villis aids in movement of lymph * carries lipids (chylomicrons) bypassing the portal system of the liver

Question 84

Describe how to identify the ilium from other sections of the small intestine?

Answer 84

Identification of the iluim Only the ilum has Peyers patches small masses of lymphatic tissue found throughout the ilium within the submucosa layer.

Question 85

Describe the unique histology of the below structure ?

Answer 85

Colon, caecum and rectum primary function is the reabsorption of water and inorganic salts Mucosa * No plicae circulares or intestinal villi (this means the epithelium is much smoother) * many crpts of Lieberkuhn packed with goblet cells * laminar propria is very thin. * muscularis mucosa is very thick Sumbmucosa * contains a varyable amount of fat and blood vessels Muscularis externa * the two layers are much thicker when compared to other sections of the gastrointestinal tract

Question 86

Describe how the intestine changes as it progresses along from the small to large intestine ?

Answer 86

Question 87

Discuss the three overlapping periods of Haematopoiesis (blood cell formation)

Answer 87

Blood cell formation, Haematopoiesis Blood cell fromation is started by haemangioblast in the visceral mesoderm. (Splanchnic mesoderm of the yolk sac wall). Three periods **Mesoblastic** = blood island - formation of blood vessels and first blood cell erthrocyte (vasculogenesis and erythropoiesis) **Hepato - lienal period =** The liver becomes the main heematopoietic organ at about f months of gestation, at 3-7 months the spleen in ruminants. **Medullary period =** Bone marrow begins haematopoetic activity around 4 months of gestation.

Question 88

Describe the formation of the cardiac tube, and the first fold?

Answer 88

Blood islands (cardiogenic field). During embryo folding the blood islands fold to become two dorasl and ventral aortae, and venous system In parallel the blood islands undergo a lateral folding to form the cardiac tube. * Blood islands/endothelial tubes move to the midline to fuse forming the cardiac tube. (lateral fold) * Endothelial tube * At its posterior end the heart will be joined with the venous system, then heart formation occurs. (cranial fold) * embryonic heart beat begins at day 22 pig, day 23 dog and day 24 horse.

Question 89

Name the three overlapping periods of blood cell formation ?

Answer 89

Three overlapping periods of blood cell formation 1. Mesoblastic 2. Hepato-lienal 3. Medullary period

Question 90

Describe the segmentation of the cardiac tube ?

Answer 90

Segmentation of the heart Too develop into a four chambered heart it first develops into a loop formation than undergoes an internal division.

Question 91

Name the segments of the heart tube ?

Answer 91

Bulbous cordis = becomes the ventricular septum sinus venosus truncus arteriosus

Question 92

Describe the embryonic loop formation of the heart ?

Answer 92

Loop formation * primitive atrium loops around ontop of the primitive atrium * the bolbus cordis moves inbetween

Question 93

Describe the development of the sinus venosus ?

Answer 93

Heart formation sinus venosus * Three pairs of veins are connected to the sinus venosus (vitelline vein, umbilical vein and cardinal vein. * The three veins form left and right horns * The right horn is favored and merges with the atrium develops into the cranial and caudal vena cava * The left sinus horn develops into the coronary sinus

Question 94

Name the structures of the right ventricle and right atrium ?

Answer 94

Question 96

Describe the septum formation in the atrium ?

Answer 96

Septum formation in the atrium septum primum, foramen primum, septum secundum, foramen secundum foramen ovale * **Septum primum** develops from the roof of the atrium * The **Foramen primum** provides passage for the blood between right and left atrium * Before the **foramen primum** seals over, holes develop called the **foramen secundum** A **septum secundum** grows to the left of the septum primum, and grows until it completely covers the foramen secundum, but retains the **foramen ovale** during embryonic development.

Question 97

Describe the two atrial defects of the Foramen secundum, and septum secundum ?

Answer 97

Atrial defects 1. Foramen secundum and septum primum develop too large. When the two septa joined at birth the two overlap the holes. 2. Septum secundum secondum failed to develop, thus septum primum cannot seal and the deoxygenated and oxygenated blood mix.

Question 98

Describe how the four chambers of the heart are formed ?

Answer 98

Formation of the septums Septum intermedium * endocardial cushions in the cardiac wall grow until they meet and fuse forming the septum intermedium. * division between atria and ventricles Interventricular septum * Transition between the bulbus cordis and ventricule is marked by a mascular fold which develops into the interventricular septum. * grows dorsally towards the septum intermedium Now we have a four chambered heart

Question 99

Describe the formation of the pulmonary and aortic trunks (aorticopulmonary septum) ?

Answer 99

Aorticopulmonary septum The trunks arise from the bulbous cordis and truncus arteriosus * these are then divided into two oposing channels by bulbar/truncal cushions in the walls of the heart * these fuse in the midline to form a spiralling septum * base of right ventrical of the heart giving rise to the left and right pulmonary arteries

Question 100

Describe the development of the atrioventricular valves ?

Answer 100

Atrioventricular valves * The atrioventricular valves arise from the edges of atrioventricular channels and are suspended by muscular cords * the left has two valves the mitral/ bicupsid valve * the right has three valves the tricupsid valve * The muscular cords which attach to the valves are replaced by the connective tissues **(chordae tendinae),** and the rest becomes papillary muscle.

Question 101

Describe the development of the semilunar valves ?

Answer 101

Describe the formation of semilunar valves ? * The semilunar valves develop as swellings of the truncus arteriosus, into the ventral aorta and pulmonary trunk via growing cushions. * Upon completion of the aorticopulmonary septum, the swellings give rise to three half moon shaped valves in each aortic and pulmonary outlet.

Question 102

Describe the development of the arterial and venous systems ?

Answer 102

Arterial and venous systems **Arterial system** * Cranial; six aortic arches, dorsal and ventral aorta * Caudal; at first they extend as a pair then fuse to form a single aorta, and develop into internal and exdternal iliac arteries. **Venous system** * returns blood to the heart * vitteline vein (veins from yolk sac and abdominal organs) * Umbilical vein (veins from placenta oxygenated blood) * Cardinal veins (veins from the cranial part of the developing embryo)

Question 103

Describe foetal circulation

Answer 103

Foetal circulation * Circulation in the foetus is designed so that blood bypasses the liver (ductus venosus), due to there being no requirement to metabolise nutrients * Foetal circulation also bypasses the lungs (ductus arteriosus), as the lungs are undeveloped * the foetus meets all its nutrient and oxygen requirments from the maternal blood across the placenta.

Question 104

Describe the major changes to foetal circulation that occur at birth ?

Answer 104

Two major events occur to the circulation at birth Placental blood flow ceases Lung respiration begins * Unbilical arteries closes to form ligamentum teres vesicae * umbilcal veins closes to form ligamentum teres hepatis * ductus venosus closes to form ligamentum venosum * ductus arteriosus closes to form ligamentum arteriosum * foramen ovale closes to form the fossa ovalis

Question 105

Describe the formation of the gut tube ?

Answer 105

Gut tube formation * endoderm * the trilaminar germ disc undergoes a lateral folding of the developing embryo * the disc starts to resemble a tube * internal layer of endoderm lies on the innermost aspect of this tube to form a primitive gut tube from mouth to anus * endoderm forms the respiratory and digestive system

Question 106

Classifcation of the primitive gut ?

Answer 106

The primitive gut can be classified into free sections * the endoderm lined tube may be classified into the foregut, midgut and hindgut * the respiratory system develops from a region known as the foregut * respiratory diverticulum

Question 107

Describe how the respiratory diverticulum develops ?

Answer 107

Respiratory diverticulum * The respiratory oesophagus is seperated from the trachea and oesophagus by the **tracheo-oesophageal groove.** * that results in the edevlopment of the **tracheo-oesophageal septum** which defines the **respiratory diverticulum** * The respiratory diverticulum has branched to form left and right lung buds as the precursors of left and right lung tissues.

Question 108

Identify two Trachea-oesophageal defects which occur during development?

Answer 108

Tracheal oesophageal defects **Altresia** * an abnormal closure of a tube orifice * often associated with oesophageal atresia **Fistula** * an abnormal opening between two tubes * occurs when the oesophgeal septum fails to develop correctly

Question 109

Name the four periods of the lung maturation ?

Answer 109

The four periods of lung maturation 1. Pseudo-glandular period 2. Canalicular period 3. Saccular period 4. Alveolar period

Question 110

Describe the pseudoglandular period of lung development ?

Answer 110

Pseudoglandular period of lung development * terminal bronchioles form * lungs resemble glands under the microscope, as tubules lined by columnar endodermal epithelium. * structures often mistook for glands

Question 111

Describe the canicular period of lung development ?

Answer 111

Canicular period * second stage of lung development * terminal bronchioles branch too form two or more respiratory bronchiloes * lined by columnar endodermal epithelium * surrounding capillaries grow intensely from the mesoderm, and make close contact with the epithelium A foetus born during this period would not survive as respiration is impossible.

Question 112

Describe the saccular period of lung development ?

Answer 112

Saccular period * Alveoli sacs develop as the last birufication as blind saccules * alveolar sacs begin to thin from columnar to squamous epithelium A premature birth at this stage may result in respiratory distress syndrome and the baby has a slime chance of survival.

Question 113

Describe the alveolar period of development ?

Answer 113

Alveolar period of lung development * Final compartment development for gas exchange * capillaries bulge into the alveoli sacs forming immature aveoli * epithelial cells differentiate into type one and two pneumocytes A foetus born during the alveolar stage would have a good chance of survival

Question 114

Describe the formation of the pleural cavities ?

Answer 114

Pleural cavities * Lateral folds of the lateral mesoderm differentiate into the parietal and vsiceral layers of the pleura * the space between is the intraembryonic mesoderm * Intraembryonic coelom = pleural and peritoneal cavities * extraembryonic coelom = develops into the chorionic cavity that is outside of the developing embryo, to form the placenta. The result is the **splanchnic mesoderm** touches the lungs directly and runs in all the fissures (Visceral pleura) The **somatic mesoderm** is reflected at the lung root and adhers to the thoracic wall and diaphragm (parietal pleura)

Question 115

Name the three embryonic components that give rise to the diaphragm ?

Answer 115

The three embryonic components of the diaphragm 1. pleuro-peritoneal membrane 2. body wall musculature 3. septum transversum

Question 116

Describe how the septum transversum contributes to the diaphragm ?

Answer 116

Septum transversum - diaphragm * formed during the head and tail folds of the embryo * thick mass of mesenchymal cells * it forms a partial shelf seperating the thorax and abdomen

Question 117

Describe the contribution of the pleuro-peritoneal membrane to diaphragm development ?

Answer 117

Pleuro-peritoneal membrane * The thorax communicates with the abdomen through **pericardial peritonial canals** * Pleuro-peritoneal membrane grows from the dorsal body wall to seal off the canals and form tendinous part of the diaphragm.

Question 118

Describe the contribution of the body wall masculature to diaphragm development ?

Answer 118

Body wall masculature * The lungs grow in size and push some of the lateral wall inwards as a final musculature component of the diaphragm * This ingrowth forms the final part of the diaphragm.

Question 119

Describe the embryological origins of the oral cavity, anus and urogenital openings.

Answer 119

Embryological origins Oral cavity * ectodermal depression * stomoderm (oral pharyngeal membrane) Anus and urogenital opening * ectodermal depression * proctoderm (cloacal membrane)

Question 120

Describe the blood supply to the gut during embryonic development ?

Answer 120

Gut blood supply Foregut = coeliac artery Midgut = cranial mesenteric artery Hindgut = caudal mesenteric artery

Question 121

Describe the embryonic origins of a mesentary ?

Answer 121

Mesentary * Formas when a layer of peritoneum lies against each other a double layer of peritoneum, - lateral mesoderm * contains blood vessels, nerves and lymphatics * attaches an organ to the body wall Lesser mesentary - lesser curvature of stomach, dudenum and liver Greater mesentary - spleen and the greater curvature of the stomach

Question 122

Describe the embryological origin of the foregut ?

Answer 122

Foregut Oesophagus * extends developing pharynx to stomach * start wide + short to long and narrow * stratified squamous epithelium Stomach * forms from a dilated region of the foregut * rotates 90degress clockwise with dorsal surface on the left * dorsal surface grows faster than the ventral surface forming the greater and lesser curvatures of the stomach respectively * finally 45-90 degree clockwise rotation to form the pylorus - to raise the pylorus and lower the cardia descending duodenum and accessory organs are also a part of the fore gut.

Question 123

Describe the embryological orgin of the liver ?

Answer 123

Foregut accessory organ liver? * Hepatic diverticulum = consist of hepatic cords, cystic diverticulum, and the ventral pancreatic bud of cells from the endoderm * they envade to the mesoderm of the septum transversum of the diaphragm to form the cellular component of the liver * endoderm forms the tubular part of the liver

Question 124

Describe the embryological development of the midgut ?

Answer 124

Midgut the midgut develops into the ascending duodenum, jejunum,iliem, caecum, ascending colon and 2/3 along the transverse colon The midgut is suspended from the dorsal wall by the root of the mesentary **It communicates or opens to the yolk sac via the vitelline gland.**

Question 125

Describe the embryological origins of the gallbladder ?

Answer 125

Gall bladder * Develops from the hepatic diverticulum - cystic diverticulum * forming the gall bladder and cystic duct The cystic portion fails to develop in the horse, whale and rat

Question 126

Describe the embryological origin of the pancreas ?

Answer 126

Pancreas * A ventral pancreatic bud is derived from the hepatic diverticulum * a dorsal pancreatic bud emerges from the foregut dorsally The ventral pancreas rotates with the stomach and eventually fuses with the dorsal pancreatic bud.

Question 127

Describe the developments and differential growth of the midgut ?

Answer 127

Midgut Development * R vitelline artery gives rise to the cranial mesenteric artery (blood circulation to/ from yolk sac of foetus) which becomes internalised in the loop * proximal descending part becomes small intestine * distal ascending part becomes the large intestine Mid gut differentiation * a rapid extension of the proximal part pushes to the right and wraps around the cranial mesenteric * 180 degree rotation around dorsal axis * continues to move through to the left then cranially again (completed 360 degree rotation)

Question 128

Describe the positioning of the midgut after final development ?

Answer 128

Mid gut positions once developed ## Footnote Ascending duodenum and descending colon = right jejunum = ventral left caecum and iliem = right ascending colon = right, two dimensional loops ruminants, spiral coil pig, narrow U shape loop horse Transverse colon = becomes localised right to left and continues into descending colon

Question 129

Describe the branches of the cranial mesenteric artery ?

Answer 129

Question 130

Describe the development of the hind gut ?

Answer 130

Hind gut = distal 1/3 transverse colon, desending colon, rectum and anal canal ## Footnote Cloacal membrane = Forms the terminal part of the hindgut where the endoderm comes to lie in contact with the ectoderm. Urorectal septum - develops into perineal body - to divide the rectum and cloaca

Question 131

Identify the three generations of kidney primordia ?

Answer 131

Three kidney primordia * pronephros (early nephrons) * mesonephrons (middle nephrons) * metanephrons (later nephros)

Question 132

Describe the development of the pronephrons ?

Answer 132

Pronephrons form from intermediate mesoderm in the cervical region * early development * cranial region * consist of 7-8 pairs pronephric tubules * in lower vertebrates - amniotes (tetrapods) comprising reptiles, birds and mammals * only 1-3 tubules form and connect to archinephric duct Duct will continue to develop caudally to the cloaca. * mammals = degenerate without function * fish =persist and functions in immature fish * amphibians = persist and function in larvae

Question 134

Describe the development of the mesonephrons ?

Answer 134

Mesonephrons * forms glomeralus, tubules and bowmans capsule * size correlates to placenta type - big with high placenta layers * cranial mesophrinic tubules connect with the developing gonads * mesonephric duct connected to epididymis and vas deferens in male Forms by intermediate mesoderm in the lumbar and thoracic area * mammals function as temporary embryonic kidney * birds reptiles function until hatching * fish + amphibians function as adult kidney

Question 135

Describe the development of the metanephros ?

Answer 135

Metanephros Derives from the **metanephric diverticulum** Derived from intermediate mesoderm in the pelvic region * branches from archinephric duct and mesoephric duct * loacted sacral region * induces differentiation of renal tubules Become the permanent functional kidneys in mammals

Question 136

Describe the development of the ureteric duct

Answer 136

Ureteric duct Suquential division of the ureteric duct forms the * collecting ducts * major calyces * minor calyces * renal pelvis * ureter

Question 137

Describe the devlopment of the metanephric blastema ?

Answer 137

Question 138

Describe the ascent of the kidneys ?

Answer 138

Ascent of the kidneys * kidneys move cranially into the lumbar region * rotate 90 degress to face the veertebrae * initially hilum is the entry area of blood vessels * blood supply from aorta changes as the kidneys ascend

Question 139

Describe the formation of the bladder ?

Answer 139

Formation of the bladder * terminal part of hindgut extends into the cloaca * divided into the anus and **urogenital sinus** * urinary bladder derived from endoderm * canal near the cloaca called urachus and pelvic region of urogenital pelvis

Question 140

Describe Leydig and Sertoli cells

Answer 140