Endocrine System Lecture

Question 1

Endocrine system

Answer 1

• Synthesis and secretion of chemical messengers called hormones. Hormones are distributed throughout the body via the bloodstream, affecting specific target cells and organs, or a wide range of cells, organs, and tissues.

Question 2

Hormones

Answer 2

Biological substances which act on specific target cells

Question 3

Endocrine control

Answer 3

Hormone is secreted into the blood stream and has systemic effects on cells expressing specific receptors

Question 4

Autocrine control

Answer 4

Cell secreting the hormone has receptors on its surface for that hormone (self stimulation)

Question 5

Paracrine control

Answer 5

Secreted hormone acts on adjacent cells expressing specific receptors

Question 6

Three classes of hormones

Answer 6

Steroids
Amino acids and Arachidonic acid analogs
Peptides

Question 7

Steroids

Answer 7

• Testosterone, estrogen, progesterone

Question 8

Amino acids and Arachidonic acid analogs

Answer 8

• Nor-epinephrine, epinephrine, prostaglandins, prostacyclans, leukotrienes, thyroid hormones

Question 9

Peptides

Answer 9

• Adrenocorticotrophic hormone (ACTH), follicle stimulating hormone (FSH), Leutenizing hormone (LH), insulin, glucagon, growth hormone (GH), antidiuretic hormone (ADH), interleukins, oxytocin, various additional growth factors

Question 10

List the organs of the endocrine system.

Answer 10

– Pineal gland
– Pituitary gland
– Hypothalamus
– Thyroid gland
– Parathyroid glands
– Adrenal gland
– Endocrine pancreas

Question 11

Identify the microanatomy of the pineal gland including its location, function, primary cell type, and hormones secreted

Answer 11

– “Pine cone-shaped” organ covered with pia mater. Penetration of connective tissue into interior to form lobules. Contains cells called pinealocytes
* Pinealocytes
* Primary cell population
* Large cells arranged in cords or clumps
* Round, open-faced nuclei
* Acidophilic granules
* Secretes melatonin and serotonin
* Glial cells
* 5% of cell population
* Similar to astrocytes
* Corpora arenacea (“brain sand”, psammona bodies, acervuli)
* Concentric layers of calcium and magnesium phosphate surrounding organic matrix of carrier proteins released with pineal secretions (*Radiodense – useful as markers in diagnostic imaging)
* Fenestrated capillaries
* Melatonin

Question 12

Explain the effects of melatonin on the body.

Answer 12

– Released during darkness (night)
– Inhibits steroidogenic activity of gonads
– Regulates circadian rhythms (humans – influences onset of puberty, body rhythms, plays a role in “jet lag” during long flights; animals – control of estrous cycles and seasonal breeding, controls changing skin color of reptiles and lower vertebrates)

Question 13

Describe the microanatomy of the pituitary gland including its location, function, main cell types and hormones secreted.

Answer 13

Composition
– Anterior lobe
– Posterior lobe
* Anterior lobe (evagination of ectoderm from oropharynx – Rathke’s pouch)
– Pars distalis
* Majority of anterior lobe
* Capsule of collagenous and reticular tissue
* Cells (chromophobes, acidophils, basophils) organized into cords/clusters
* Pars distalis
– Chromophobes
* Small, round cells
* Scant, poorly stained cytoplasm
* Unknown function
– Acidophils
* Larger cells
* Acidophilic granules
* Somatotropes (produce GH)
* Lactotropes (produce prolactin [PRL])
* Pars distalis
– Basophils
* Larger cells
* Thyrotropes
– Secrete TSH
* Corticotropes
– Secrete propiomelanocorticotropin (POMC) which becomes ACTH, MSH, β-endorphin, enkephalin, β-lipotropic hormone
* Gonadotropes
– Secrete FSH, LH

Question 14

Growth hormone (GH)

Answer 14

–> In this phase of development, growth hormone promotes the growth of bone and cartilage. Throughout life, growth hormone regulates the fat, muscle, tissue and bone in our bodies, and other aspects of our metabolism such as insulin action and blood sugar levels.

Question 15

Thyroid stimulating hormone (TSH)

Answer 15

Thyroid hormones affect nearly every organ in your body, including your heart. They help control your weight, body temperature, muscle strength, and even your mood. If you don’t have enough thyroid hormones in your blood, many of your body functions slow down. If you have too much, many body functions speed up

Question 16

Adrenocorticotropic Hormone (ACTH)

Answer 16

–> Adrenocorticotropic hormone (ACTH) is produced by the pituitary gland. Its key function is to stimulate the production and release of cortisol from the cortex (outer part) of the adrenal gland.

Question 17

Describe the blood supply to the pituitary gland.

Answer 17

• Blood Supply
  – Cranial/Superior hypophyseal artery (supplies pars tuberalis, median eminence, infundibulum)
• Primary capillary plexus (absorbs releasing factors secreted by median eminence of) hypothalamus
• Hypophyseal portal veins (connects primary and secondary capillary plexuses; transports releasing factors to cells of pars distalis)
• Secondary capillary plexus (supplies blood containing releasing factors to cells of pars distalis, stimulates release of hormones including ACTH, MSH, FSH, LH, TSH)
  – Caudal/Inferior hypophyseal artery (supplies pars nervosa)

Question 18

Define the role the hypothalamus plays in the control of pituitary gland.

Answer 18

Regulation of pituitary gland secretion:
* Release of regulating hormones from the hypothalamus
– Secretion of releasing and inhibitory hormones from cells of hypothalamus into hypophyseal-portal veins in response to circulating levels of systemic hormones and input from the CNS.
– Predominantly effects cells of the anterior pituitary.
* Paracrine and autocrine secretion
– Release of hormones from cells located within the pituitary gland.
* Feedback regulation of circulating hormones
– Levels of circulating hormones regulates hormone release from the anterior pituitary (negative feedback – the high levels of circulating hormones inhibits further release of these hormones).

Question 19

Describe the microanatomy of the thyroid gland including its location, function, primary cell types, and hormones secreted.

Answer 19

• Location
  – Caudal/ventral to larynx
• Origin
  – Pharyngeal endoderm
  – Function
  – Influences metabolism, heat production, body growth and development
• Structure
  – Bilobed (lobes connected by a tissue bridge [isthmus] in humans)
  – Covered by loose connective tissue that penetrates organ to provide support [perifollicular connective tissue contains lots of reticular fibers]
  – Hundreds of thousands of follicles (follicular cells surrounding gel-like mass [colloid])
• Parafollicular (C) Cells
  – Pale staining
  – Organized individually or as clusters
  – Contained within follicle, but have no contact with lumen
  – Produce calcitonin

Question 20

Calcitonin

Answer 20

– An antagonist to PTH
– Important calcium regulator in animals; less important in humans
– Secreted in response to high blood calcium levels
– Inhibits osteoclast activity
– Stimulates calcium deposition in bones

Question 21

T3
–

Answer 21

Secreted by follicular cells
– Secretion is regulated by TSH from pars distalis of anterior pituitary
– Released in small amounts
– More potent, metabolically active form of thyroid hormone
– Stimulates cell and tissue metabolism
– Influences heat production
– Stimulates body growth and development, especially nervous system

Question 22

T4

Answer 22

Low metabolic activity (low affinity receptor binding)
– Stimulates cell and tissue metabolism
– Influences heat production
– Stimulates body growth and development, especially nervous system

Question 23

Define the microanatomy of the parathyroid glands including its location, function, main cell types, and hormones secreted.

Answer 23

• Origin
  – 3rd and 4th pharyngeal pouches
• Location
  – Usually 2 pairs (internal and external pairs in animals; external location in humans) associated with superior/cranial and inferior/caudal portions of thyroid lobes.
• Structure
  – Small, round to oval glands
  – Covered by loose connective tissue capsule (external location) or loose connective tissue septa of thyroid gland (internal location)
  – Separated into poorly defined lobules (humans) or cords, clusters, strands, sheets, rosettes (animals)
  – Numerous capillaries
  – Chief cells
• Small polygonal cells
• Central nucleus
• Pale staining acidophilic cytoplasm
• Secretion of parathyroid hormone (PTH)
  – Oxyphil cells (humans, horses, cattle)
• Large cells
• Granular, acidophilic cytoplasm
• Unknown function

Question 24

parathyroid hormone

Answer 24

produced by the thyroid glands helps maintain the right balance of calcium in the bloodstream and in tissues that depend on calcium for proper functioning. This is especially important for nerve and muscle function, as well as bone health.

Question 25

Explain the effects of PTH on the body.

Answer 25

– 84 amino acid polypeptide – Stimulates increase in blood calcium levels * Stimulates bone remodeling * Increases tubular reabsorption of calcium by the kidneys * Increases excretion of phosphate by the kidneys * Increases conversion of 25-OH vitamin D3 to hormonally active form 1,25-(OH)2 vitamin D3 * Increases calcium and phosphate absorption by the small intestine

Question 26

Decribe the microanatomy of the adrenal gland including its location, function, primary cell types, and hormones secreted.

Answer 26

* Origin – Mesoderm (cortex) and neural crest ectoderm (medulla) * Location – A single, small gland situated near the superior/cranial pole of each kidney, within the retroperitoneal space. * Structure – Dense connective tissue capsule – Cortex * Fine collagenous and reticular fibers * Polyhedral secretory cells arranged into cords (2 cell thickness) extending radially from the medulla * Zona glomerulosa * Zona fasciculata * Zona reticularis – Hormones = epinephrine, norepinephrine, androstenedione, aldosterone, cortisol

Question 27

– Epinephrine and Nor-epinephrine

Answer 27

* Increase heart rate * Increase strength of heart contractions * Increase blood pressure * Decrease blood flow to viscera and skin * Dilation of pupils * Dilation of respiratory passages * Decreased urine output * Decreased digestive system activity

Question 28

– Aldosterone

Answer 28

* Generated from cholesterol * Acts on principal cells of distal kidney tubules, gastric mucosa, salivary glands, sweat glands where it stimulates reabsorption of Na+. * Also promotes excretion of K+ by the kidneys.

Question 29

– Cortisol

Answer 29

(*overall increased blood glucose levels with decreased peripheral glucose utilization) * Stimulates conversion of amino acids to glucose * Promotes uptake of amino acids and fatty acids * Stimulates polymerization of glucose to glycogen in the liver * Stimulates breakdown of lipids to glycerol and free fatty acids in adipose tissue * Reduces rate of glucose utilization * Promotes oxidation of fatty acids in other tissues * Inhibits protein synthesis * Promotes protein catabolism in some cells to provide amino acids for use in glucose synthesis in the liver

Question 30

– Androstenedione

Answer 30

* Promotes development of secondary sex characteristics * Males – negligible compared to testosterone produced by testes * Females – stimulates growth of axillary and pubic hair

Question 31

Explain the microanatomy of the endocrine pancreas including its function, primary cell types, and hormones secreted.

Answer 31

* Islets of Langerhans – Scattered masses of pale-staining cells – Randomly distributed throughout organ – Islets cells (*not differentiated with H&E staining) * Alpha cells – Secrete glucagon * Beta cells – Secrete insulin – Most numerous Islet cell in humans and dogs * Delta cells – Secrete somatostatin * Minor cells – Secrete Ghrelin, secretin, vasoactive intestinal peptide (VIP), substance P, Motilin, Pancreatic polypeptide,

Question 32

– Glucagon

Answer 32

* Stimulates release of glucose into blood stream * Stimulates gluconeogenesis (synthesis of glucose from metabolites of amino acids) and glycogenolysis (breakdown of glycogen) * Mobilizes fats from fats cells (lipolysis) * Stimulates hepatic lipase * Stimulates protein breakdown (proteolysis) to promote gluconeogenesis

Question 33

– Insulin

Answer 33

* Stimulates uptake of glucose from the circulation * Stimulates storage of glucose via formation of glycogen (glycogenesis) * Promotes glucose utilization within cells (glycolysis) * Stimulates breakdown of chylomicrons and other LDLs into free fatty acids (lipogenesis) * Stimulates protein synthesis in skeletal muscle and liver cells

Question 34

– Somatostatin (GH)

Answer 34

* Similar to GH secreted by hypothalamus * Islet GH can inhibit insulin and glucagon secretion, and suppress exocrine secretion of pancreas