Week 11: The Integumentary and Lymphatic System

Question 1

Functions of the lymphatic system

Answer 1

1. Drainage of excess interstitial fluid: Lymphatic vessels drain excess interstitial fluid from tissue spaces and return it to the blood. This function is closely linked with the cardiovascular system
   
   • Tissue spaces: Interstitial fluid
     2. Transports lipids and lipid soluble vitamins from the gastrointestinal system into the blood
   • Some molecules are too large to go into the blood, so lipids enter into lymph vessels as they are larger which perfuse in and can be absorbed into the bloodstream
     3. Carries out immune responses: Lymphatic tissue initiates highly specific responses directed against foreign/abnormal cells. Transports immune cells and antigens to lymph nodes to be ‘checked’ and/or destroyed (adaptive immune responses)
     Specialized tissue

Question 2

Components of the lymphatic system:

Answer 2

• Lymphatic fluid: Clear fluid, originating from blood plasma, moves from interstitial space between body tissues/cells (interstitial fluid) into lymphatic vessels (lymph), comes from blood plasma, moves from interstitial space (space between tissues/cells)
  
  • Lymphatic vessels: The means by which lymph travels around the body
  • Lymphatic organs and tissues e.g. lymph nodes
  • Composed of a type of connective tissue that contains large numbers of lymphocytes
    B and T lymphocytes: Involved in adaptive immune response

Question 3

Lymphatic organs and tissues:

Answer 3

• Classified into two groups based on their functions:
  Primary lymphatic organs:
  
  • The site where stem cells divide and become capable of mounting an immune response
  • Red bone marrow and thymus
  • Production of mature B lymphocytes and (immature) Pre-T lymphocytes
  • Immature as they have to travel to the lymph node before they mature/destroy
    Secondary lymphatic organs and tissues
  • The site at which the most immune response occur
    Lymph nodes, spleen, lymphatic nodules/follicles

Question 4

Lymph nodes:

Answer 4

• Small bean shaped tissues comprised of specialized connective tissue
  
  • Approximately 600 in the body
  • Located along the lymphatic vessels and commonly in groups
  • Largest groups present near mammillary glands, axillae and groin
  • Lymph enters through afferent vessels: Passes through the node: and leaves via efferent vessels
  • Lymph nodes function to trap foreign substances within the node:
  • Initiation of adaptive response
  • B and T lymphocytes
  • Autoimmune response: Immune cells accidentally something being foreign as the immune system reacted in a wrong way e.g. psoriasis, coeliac

Question 5

Lymphatic transport:
Lymphatic vessels

Answer 5

• Begin as lymphatic capillaries that are closed at one end
  
  • Have greater permeability than blood permeability so they can absorb large molecules like proteins and lipids
  • Bluntly ended
  • More permeable than blood vessels, walls have large gaps so fats/large particles can drain back
  • Many lymphatic capillaries unite to form larger lymphatic vessels
  • These resemble small veins in structure, however they gave thinner walls and more valves
  • Lymphatic vessels will then converge into lymphatic trunks, and then into ducts before draining into venous blood
    Valves to catch it a prevent it from going out

Question 6

Lymphatic circulation:

Answer 6

Sequence of fluid flow:
Blood capillaries (blood) > interstitial spaces (interstitial fluid) > Lymphatic capillaries (lymph) > Lymphatic vessels (lymph) > Lymphatic trunks and ducts (lymph) > venous return to the heart (blood)
- Lymph nodes are scattered along the lymphatic vessels and usually occur in groups
Called a duct right before it enters back into the venous system

Question 7

Maintenance of lymph flow:

Answer 7

• The same two pumps that aid in the return of venous blood to the heart, maintain the flow of lymph
  
  • Skeletal muscles pump: Contraction of skeletal muscle causes compression of lymphatic vessels, propelling lymph upward. Valves within lymphatic vessels function to stop back-flow of lymph
    Respiratory pump: Lymph flow is driven by pressure changes that occur during inspiration/inhalation. When pressure in the thoracic cavity decreases (due to increase in volume) lymph flows in from regions of higher pressure e.g. the abdominal region to follow the pressure gradient

Question 8

Skin and Appendages:

Answer 8

• Skin covers the entire surface of the body (cutaneous membrane)
  
  • Variable in thickness depending on location
  • Largest organ of the body: Covers an area of 2 square meters and total weight of 5 kilograms
    Thick in heels

Question 9

Key functions: Skin

Answer 9

• Maintain physical integrity
  
  • Maintain biochemical integrity
  • Thermoregulation
  • Sensory feedback
    Information to CNS about surrounding environment

Question 10

Division: Skin

Answer 10

• Epidermis: Epithelial tissue, sits superficially (surface that we see)
  
  • Dermis: Connective tissue
  • Hypodermis: Not part of the skin, rather it is composed of areolar and adipose tissue

Question 11

Overview of the Epidermis

Answer 11

• Keratinized stratified squamous epithelium
  As it is epithelial it is avascular

Question 12

4 cell types: Epidermis

Answer 12

• Keratinocytes
  
  • Melanocytes
  • Intraepidermal macrophages
    Tactile epithelial cells

Question 13

Keratinocytes:

Answer 13

• Make up 90% of the epidermis
  
  • Make Keratin
  • Provide strength and protection
  • In particular layers through the skin
    Attach protein that serves to protect the skin and underlying tissue and waterproofing the skin

Question 14

Melanocyte:

Answer 14

• 8% of the cells in the epidermis
  
  • Produce Melanin (pigment) to protect from UV light
    Found in the basal layer of the epidermis

Question 15

Intraepidermal Macrophage:

Answer 15

• Known as Langerhans cells
  
  • Found in the second layer of epidermis
    Ingest foreign particles

Question 16

Tactile epithelial cells:

Answer 16

• Known as Merkel’s cells
  
  • Least popular
  • Found in the basal layer
    Sensory receptors for touch

Question 17

What are the layers of the Epidermis?

Answer 17

Stratum Coreneum, Stratum Lucidum, Stratum Granulosum, Stratum Spinosum, Stratum Basale

Question 18

Stratum Corneum

Answer 18

• Most superficial layer
  
  • 20-30 layers of dead cells
  • Essentially flat membranous sacs filled with keratin
  • Glycolipids in extracellular space
  • Thick layer
    Cells are thin with no nucleus or organelles and are filled with keratin

Question 19

Stratum Lucidum

Answer 19

• The stratum lucidum is only present in very thick skin found in the fingertips, palms of the hand and the sole of feet
  
  • This layer is approx. 4-6 layers and contains clear keratinocytes
    Only present in thick skin

Question 20

Stratum granulosum

Answer 20

• Typically 5 layers of flattened cells, organelles deteriorating cytoplasm full of lamellar granules (release lipids) and keratohyalin granules
  
  • Sits in the middle of the epidermis
  • 3-5 layers of flattened cells undergoing apoptosis
    Apoptosis: Programmed cell death

Question 21

Stratum Spinosum

Answer 21

• Several layers of keratinocytes unified desmosomes
  
  • Cells contain thick bundles of intermediate filaments made of pre-keratin
  • 8-10 layers of keratinocytes
  • Top layers become more flat
  • Produce keratin
    Spinosum: appearance of the spines at the cell membrane

Question 22

Stratum Basale

Answer 22

• Deepest epidermal layer
  
  • One row of actively mitotic stem cells
  • Some newly formed cells become part of the more superficial layers
  • See occasional melanocytes and dendric cells
  • Single layer of keratinocytes
  • Cuboidal/columnar
    Cells divide and differentiate to continue production of keratocytes

Question 23

Dermis

Answer 23

• Dense irregular connective tissue layer
  
  • Collagen and elastic fibers
  • Dermis is thicker than the epidermis
  • Two major regions of dermis: Papillary region, reticular region
    Creates tensile strength and resist stretching and pulling

Question 24

Papillary region: Dermis

Answer 24

• 20% of the total dermis thickness
  
  • Finger like projections called dermal papillae
  • Anchors epidermis to dermis
  • Contains capillaries that nourish to epidermis
    Contains Meissner’s corpuscles (touch) and free nerve endings for sensations of heat, cold, pain, tickle and itch

Question 25

Reticular

Answer 25

- Dense irregular connective tissue - Attached to the hypodermis - Contains collagen, fibroblasts and elastic fibers - Provides strength, extensibility and elasticity to skin In spaced between the fibers this region contains appendages of the skin (sweat glands, blood vessels, nerves, hair follicles)

Question 26

Appendages of the skin Sweat glands

Answer 26

- Sudoriferous glands/sweat glands - Eccrine: Simple, coiled tubular glands across the body, secretory portion location deep in the dermis whereas the excretory duct passes through the dermis, epidermis and ends as a pore in the surface of the skin - These glands produce 600 mls of sweat per day - Primary function of sweat maintains thermoregulation - Apocrine: simple coiled tubular glands, bit have very large ducts and lumens and are found in armpits and groin regions - Mode of secretion is via exocytosis - Contains components when interact with bacteria on the skin surface cause a characteristic smell - Approx. 3-4 million sweat glands across the body - Responsible for releasing sweat onto hair follicles or the skin Role in the thermoregulation

Question 27

Sebaceous glands

Answer 27

- Simple branched rounded glands - Connected to hair follicles - Secretes sebum: Coats the surface of the hair and stops to from drying out and precents water evaporation and keeps skin soft and pliable - Prevents water evaporation - Softens and lubricates hair and skin Ceruminous glands: Ear wax, protect ear canal against physical damage and micro invasion - These are simple branched rounded glands, almost always connected to hair follicles - Responsible for secreting sebum which coats hair surface softening and lubricating hair and skin - Slows water loss from skin when external humidity is low Bacterial

Question 28

Hair:

Answer 28

- Presents on almost every skin surface with exception of palms and soles - Decrease heat loss - Hair offers limited protection Hair on the head decreases heat loss from the scalp

Question 29

Nails:

Answer 29

- Keratinized epidermal cells - Protect dorsal surface of distal digits - Enhance touch perception and manipulation - Covers dorsal surfaces of distal digits Provide support and pressure to palmer surface of the finge

Question 30

Lymphatic vessels:

Answer 30

- Lymphatic capillaries are located in the spaced between the cells - One-way structure enabling the fluid to enter the capillary but not leave - Lymphatic capillaries unite to form larger lymphatic vessels - Lymph nodes are located along these vessels and lymph passes through theses nodes Capillaries are blind at one end, lymphatic capillaries slightly overlap with each other to create a one way flow of fluid

Question 31

Lymphatic trunks:

Answer 31

- Lymphatic vessels form lymph trunks which drain into venous blood - Increased pressure outside the lymphatic capillary it enforces the cells to separate and interstitial fluid is able to enter the capillary. The pressure then rises on the inside and the cells rejoin with the fluid unable to re-enter the tissue - Lymphatic capillaries then join larger lymphatic vessels which are similar in structure to veins where they contain valves - Lymphatic vessels pass through lymph nodes before going into lymphatic trunks Lymphatic trunks: Drain into venous blood at the junction of the right internal jugular and right subclavian vein

Question 32

Movement of lymph in the blood:

Answer 32

- A key function of the lymphatic system is to return blood plasma and plasma proteins to the blood - Blood plasma filters through blood capillary walls, however not all components are able to filter back The excess fluid remains trapped between the cells and tissues, the body needs an efficient way to return plasma components including plasma proteins and the lymphatic system does this

Question 33

Two systems aid in the movement of lymph:

Answer 33

- Skeletal muscle pump: Occurs in normal movement. This movement compresses the lymphatic vessels and forces lymph to the junction of the internal jugular and subclavian veins - Respiratory pump: Flow is maintained by pressure changes during inhalation Gravity also helps with lymph flow with structure above the heart

Question 34

Lymph nodes:

Answer 34

- Approx. 600 nodes - Located along the lymphatic vessels - 1-25 mm in size - Lymph enters through afferent vessels, passes through the node and leaves via efferent vessels - Lymph nodes function to trap foreign substances within the node, these are then subsequently destroyed

Question 35

Skin: Position, Name of layer, type of tissue, vascularization

Answer 35

Epidermis: Superficial, Epithelial Avascular Dermis: Connective tissue, vascular Hypodermis (subcutaneous layer): Deepest, Loose areolar tissue with predominance of adipose cells, vascular

Question 36

What is vascular and avascular?

Answer 36

Vascular: contains blood vessels for the transport of fluids Avascular: Lacks blood vessels and does not transport blood

Question 37

Thermoregulation

Answer 37

- The release of sweat from sweat glands and its evaporation lowers body temperature - Constriction of surface vessels reduces flow of blood in the dermis, reducing heat loss to the external environment - During moderate exercise, more blood is directed through the superficial vessels of the dermis, helping to lower body temperature With extreme exercise, blood is preferentially shunted away from the skin, to muscles and therefore body temperature rises

Question 38

Blood reservoir:

Answer 38

The skin contains an extensive network of blood vessels and therefore is capable of storing blood which can be diverted to other body areas when required

Question 39

Protection:

Answer 39

- The skin provides a physical, chemical and biological barrier - Tight cell junctions prevent bacterial invasion - Lipids released retard evaporation - Pigment protects somewhat against UV light Langerhans cells alert immune system

Question 40

Cutaneous sensations:

Answer 40

- Touch, pressure, vibration, tickle, heat, cold and pain arise in the skin

Question 41

Synthesis of Vitamin D

Answer 41

- UV light activates a molecule in the skin to a precursor of Vitamin D - This activated precursor is then modified by enzymes in the liver and kidneys to produce calcitriol, the most active form of Vitamin D Vitamin D is necessary for the absorption of calcium from food in the gastrointestinal tract

Question 42

Excretion

Answer 42

The skin excretes 400 ml of water/day, small amounts of salt, Co2, ammonia and urea

Question 43

Hair shaft:

Answer 43

Present on almost every skin surface with exception of palms and soles in humans it offers very little protection

Question 44

Arrector Pili muscles

Answer 44

- These muscles are innervated by the sympathetic nervous system - Activation of the arrector pili muscles causes hair follicles to stand up This assists in trapping heat close to the surface of the skin

Question 45

Eccrine sweat glands

Answer 45

- There are approx. 304 million sweat glands across the body - Responsible for releasing sweat onto either hair follicles or the skin surface - 2 main types of sweat glands are eccrine glands and apocrine sweat glands - Eccrine glands are made up of coiled secretory part that lies within the reticular layer of the dermis The tubular excretory part opens on to the skin surface facilitating the sweat glands role in cooling for temperature regulation

Question 46

Apocrine sweat glands

Answer 46

- Limited to specific areas of the axilla (armpit) and anogenital areas - Ducts open into the hair follicles Secretion is true sweat, fatty substances and protein (merocrine) thus more odorous

Question 47

The reticular region of the dermis

Answer 47

- Dense irregular connective tissue - Attached to the hypodermis - Contains collagen, fibroblasts and elastic fibers - Provides strength, extensibility and elasticity to skin - In spaces between the fibers this region contains 'appendages of the skin' - The following structures are considered appendages of the skin - Sudoriferous glands (sweat glands), eccrine glands, apocrine, ceruminous glands, mammary glands Sebaceous glands, hair and hair follicle, nail

Question 48

Dermis:

Answer 48

- The dermis is deep to the epidermis but is thicker than the epidermis - The dermis is a dense irregular connective tissue layer, heavily embedded with collagen and elastic fibers - Collagen in the dermis is important as it has the ability to resist longitudinal stress - It is also cross linked to provide good multidirectional strength - Elastin is important in the dermis as it gives skin the ability to stretch and recoil, due to its randomly coiled structure - It gives skin is rubbery resilient quality Papillary and reticular region

Question 49

The Papillary region of the dermis

Answer 49

- Accounts for 20% of the total dermis thickness - Fingerlike projections that are called dermal papillae - Anchors epidermis to dermis - Increase surface area - Contains capillaries that feed epidermis Contains Meissner's corpuscles (touch) and free nerve endings for sensations of heat, cold, pain, tickle and itch

Question 50

The integumentary and lymphatic systems:

Answer 50

- Drainage of excess interstitial tissue - Transportation of dietary lipids Immune responses

Question 51

Lymph of the fluid of the lymphatic system

Answer 51

- The body produces approx. 3 liters of excess filtered fluid per day which is managed by the lymphatic system The composition of lymph is similar to blood plasma but is also contains lymphocytes

Question 52

Lymphatic vessels

Answer 52

- Function to transport the lymph around the body and return it to the circulatory system - Lymphatic capillaries are located in the spaced between cells - The are known as blind-ended and have a one-way structure enabling fluid from the interstitial space to enter the capillary and then not leave when there is a pressure gradient - Lymphatic capillaries unite to form larger lymphatic vessels - Lymph nodes are located along these vessels where superficial lymph vessels transition into deep lymph vessels Lymphatic vessels form lymph trunks which ultimately drain into venous blood vessels

Question 53

Lymphatic tissues and organs (including lymph nodes and the spleen)

Answer 53

- Lymph nodes are the principle organ of the lymphatic system - There are approx. 600 lymph nodes in the body - They are located along lymphatic vessels of the body in loos connective tissue - Range from 1-25mm - Lymph enters through afferent vessels: passes through the node and leaves via efferent vessels Lymph nodes function as an immune checkpoint to trap foreign substances within the node: these are then subsequently destroye

Question 54

Lymphatic transport

Answer 54

- There are 2 very efficient pumping systems which allow lymphatic vessels to return to lymph to the blood a. Skeletal pump: this is a milking action when skeletal muscles move, this movement compresses the lymphatic vessels and forces lymph towards the junction of the internal jugular subclavian veins b. Respiratory pump: Pressure increases in the thoracic cavity during inhalation, applying pressure on the large lymph vessels, facilitating the flow of lymph back into the venous system Lymphatic vessels have one-way valves to prevent backflow with gravity, although gravity also helps with lymph flow for structures above the heart