(LESSON 18) Endocrine System

Question 1

Endocrine System

Answer 1

A series of ductless glands that secrete messenger molecules called hormones into the circulation. These hormones travel to distant body cells and signal characteristic physiological responses in those cells.

Controls and integrates the functions of other organ systems in the body.

Question 2

Hormones

Answer 2

messenger molecules.

Question 3

Purely Endocrine Organs

Answer 3

• primary gland: at the base of the brain
• pineal gland: in the roof of the diencephalon
• thyroid gland: in the neck
• parathyroid gland: in the neck
• adrenal gland on the kidneys
  
  • adrenal cortex
  • adrenal medulla

Question 4

Partly Endocrine Organs

Answer 4

• pancreas
• thymus
• gonads
• hypothalamus
  
  • neuroendocrine organ
• heart
• skin
• kidneys
• placenta

Question 5

Origination of most endocrine cells

Answer 5

• epithelia
• however, endocrine system is so diverse that it also includes hormone-secreting neurons, muscle cells, and fibroblast-like cells

Question 6

Classes of hormones

Answer 6

• Amino-acid based hormones
  
  • modified amino acids
    
    • amines
  • peptides
    
    • short chains of amino acids
  • proteins
    
    • long chains of amino acids
• Steroids
  
  • lipid molecules derived from cholesterol

Question 7

Basic Hormone Action

Answer 7

1. Cluster, cords, or branching endocrine cells maximizes contact with capillaries
2. Cells release hormones into extracellular space
3. Hormones immediately enter capillaries
4. Circulate throughout the entire body
5. a given hormone influences only specific tissue cells, target cells
6. Target cells’ specific recepter molecules allow hormones to bind to tissue
7. Target cell reacts in preprogrammed way

Question 8

Humoral Stimuli

(type of hormone stimuli)

Answer 8

• secrete hormones in direct response to changing levels of ions or nutrients in the blood
• humoral: relating to the blood and other body fluids
• simplest endocrine control mechanism
• ex:
  
  • cells of the parathyroid gland directly monitor concentration of calcium ions in the blood and then respond to any decline in this concentration by secreting a hormone that acts to reverse the decline

Question 9

Neural Stimuli

type of hormone stimuli

Answer 9

• A few endocrine glands are controlled this way
• ex
  
  • sympathetic nerve fibers stimulate cells in the adrenal medulla to release epinephrine and norepinephrine during flight-or-flight situations

Question 10

hormonal stimuli

type of hormonal stimuli

Answer 10

• glands that secrete their hormones in response to hormonal stimuli received from other endocrine glands.
• AKA: the purpose of some hormones is to promote the secretion of other hormones
• ex
  
  • hypothalamus secretes some hormones that stimulate the anterior part of the pituitary gland
  • Pituitary gland then secrete its hormones which stimulate hormonal secretion by other glands:
    
    • thyroid
    • adrenal cortex
    • gonads

Question 11

Feedback Loops

Answer 11

• Control hormone secretion
• Ensure that hormone concentration stay within a narrow “desirable” range in the blood

Question 12

Negative feedback loop

Answer 12

• if blood concentration declines below a minimum set point then more hormone is secreted
• if maximum set point is exceeded then hormone production is halted

Question 13

Positive Feedback loop

Answer 13

• As blood concentrations of hormones increase, the response of the effector organ stimulates further secretion
• Oxytocin:
  
  • hormone that controls the progression of childbirth
  • operates via positive feedback
  • stimulates the uterus to contract which stimulates further secretion of oxytocin

Question 14

Pituitary Gland

Answer 14

• Hypophysis: Undergrowth from the brain
• secretes at least nine major hormones
• sits inferior to the brain in the hypophyseal fossa of cella turcica of spehnoid bone
• resembles a golf club
  
  • gland forms head of club and shaft is called infundibulum.

Question 15

Infundibulum

Answer 15

• forms shaft of pituitary gland
• connects superiorly to a part of the hypothalamus called tuber cinereum

Question 16

Two basic divisions of pituitary gland

Answer 16

1. adenohypophysis: Anterior. Composed of grandular tissue
2. Neurohypophysis: posterior. composed of neural tissue and part of the brain

Question 17

Adenohypophysis

Answer 17

• Anterior
• coposed of grandular tissue
• Subdivisions:
  
  • pars distalis (anterior lobe): most anterior part
  • pars intermedia: posterior to pars distalis
  • pars tuberalis: wraps around infundibulum like a tube

Question 18

Neurohypophysis

Answer 18

• Posterior division of pituitary gland
• composed of neural tissue and part of the brain
• subdivisions
  
  • pars nervosa (posterior lobe): most inferior
  • infundibular stalk: middle
  • median eminence: cone shaped, part of hypothalamus

Question 19

Superior Hypophyseal Artery

Answer 19

• A branch of the internal carotid artery through which the artierial blood supplies the hypophysis
• supplies the entire adenohypophysis and infundibulum

Question 20

Inferior hypophyseal artery

Answer 20

• branch of the internal carotid artery
• supplies the pars nervosa

Question 21

Somatotrophic Cells

Answer 21

• The most abundant cells in the pars distalis (adenohypophysis)
• secrete Growth Hormone (GH) aka Somatotrophic Hormone (SH) or Somatotrophin

Question 22

Growth Hormone

Answer 22

• AKA Somatotrophic Hormone (SH)
• AKA Somatotrophin
• Found in Somatotrophic Cells of Pars Distalis (adenohypophyis)
• Stimulates growth of the entire body
  
  • stimulates body cells to increase protein production
  • stimulates growth of epiphyseal plates of skeleton
  • Stimulates directly
  • Also stimulates indirectly by signaling liver to secrete insulin-like growth factor-1

Question 23

Mamotrophic Cells

Answer 23

• In pars distalis of the adenohypophysis
• mamm=breasts
• secrete prolactin, a hormone that stimulates manufacture of breast milk

Question 24

Prolactin

Answer 24

• a hormone that stimulates manufacture of breast milk
• Found in mamotropic cells

Question 25

Thyrotrophic Cells

Answer 25

• In pars distalis of the adenohypophysis
• secrete thyroid-stimulating hormone (TSH), which prompts the thyroid gland to secrete its own hormone

Question 26

thyroid-stimulating hormone (TSH)

Answer 26

• secrete thyroid-stimulating hormone (TSH), which prompts the thyroid gland to secrete its own hormone
• found in thyrotropic cells

Question 27

Corticotropic cells

Answer 27

• In pars distalis of the adenohypophysis
• secrete at least two hormones that are split from a common parent molecule
  
  • **adrenocorticotropic hormone **(ACTH) stimulates the adrenal cortex to secrete hormones that help people cope with stress
  • **melanocyte-stimulating hormone **(MSH) darkens skin pigmentation by stimulating melanocytes to produce melanin

Question 28

adrenocorticotropic hormone (ACTH)

Answer 28

• stimulates the adrenal cortex to secrete hormones that help people cope with stress
• Comes from corticotropic cells

Question 29

melanocyte-stimulating hormone (MSH)

Answer 29

• darkens skin pigmentation by stimulating melanocytes to produce melanin
• comes from corticotropic cells

Question 30

Gonadotropic Cells

Answer 30

• In pars distalis of the adenohypophysis
• secrete **Gonadotropins **that act on the gonads, stimulating maturation of the sex cells and inducing the secretion of sex hormones
  
  • follicle stimulating hormone (FSH)
  • Luteinizing hormone

Question 31

Gonadotropins

Answer 31

• act on the gonads, stimulating maturation of the sex cells and inducing the secretion of sex hormones
• follicle stimulating hormone (FSH)
• Luteinizing hormone

Question 32

Tropic Hormones

Answer 32

• Hormones of the pars distalis that regulate the secretion of hormones by other endocrine glands
• TSH, ACTH, FSH, LH

Question 33

3 categories of pars distalis cell tissue

Answer 33

• when dyed and viewed by light microscopy

1. Acidophils: stain with acidic stains
   
   • somatotrophic cells
   • mammotropic cells
2. Basophils: stain with basic stains
   
   • thyrotropic
   • corticotropic
   • gonadotropic
3. Chromophobes: stain poorly
   
   • immature cells or cells depleted of hormones

Question 34

Releasing Hormones

(releasing factors)

Answer 34

• peptide hormones of the hypothalamus that secrete to control the secretion of hormones in the adenohypophysis

Question 35

Inhibiting hormones

Answer 35

• hormones of the hypothalamus that turn off the secretion of adenohypophysis hormones when necessary

Question 36

How the releasing hormones of hypothalamus signal secretion of adenohypophyseal hormones

Answer 36

• hormones are secreted from the hypothalamic neurons they enter in the median eminence of a primary capillary plexus
• Then they travel inferiorly in hypophyseal portal veins to a **second capillary plexus **in the pars distalis
• Leaving this plexus the releasing hormones attach to adenohypophyseal cells and stimulate them to secrete hormones.

Question 37

Hypothalamic-hypophyseal tract

Answer 37

• a group of axons in the neurohypophysis that arise from neuron cell bodies

Question 38

Antidiuretic Hormone

(ADH)

Answer 38

• Made in the neurons of the supraoptic nucleus in the neurohypophysis
• AKA Vasopressin (vessel constrictor)
• targets collecting ducts and distal tubules in the kidneys
• Helps body retain as much fluid as possible when thirst (dehydration) or fluid loss (severe bleeding) occurs

Question 39

Oxytocin

Answer 39

• produced in the paraventricular nucleus in the neurohypophysis
• induces contraction of the smooth musculature of reproductive organs in both males and females
• signals uterus to contract, expelling infant during child birth

Question 40

Thyroid Gland

Answer 40

• butterfly shaped
• anterior neck on the trachea, just inferior to the larynx
• has two lateral lobes (wings) connected by a median bridge (isthmus)
• largest purely endocrine gland in the body
• Produces two hormones
  
  • Thyroid Hormone
  • Calcitonin

Question 41

Thyroid hormone

(TH)

Answer 41

• Main function is to increase the basal metabolic rate
• The higher your TH secretion the higher your activity level and warmth
• the lower your TH secretion you may feel sluggish and cold

Question 42

Calcitonin

Answer 42

• secreted by parafollicular cells of the thyroid
• a protein hormone secreted when blood calcium levels are high to lower levels
• mostly during childhood. no demonstratable function in adults

*PTH and calcitonin have opposite or antagonistic effects*

Question 43

Parathyroid Glands

Answer 43

• small yellow-brown glands on the posterior surface of the thyroid gland
• remain distinct surrounded by their own connective tissue capsules
• Most people have 2 pair, as many as 8 have been reported

Question 44

Parathyroid Hormone

PTH

Answer 44

• AKA Parathormone
• a small protein hormone that increases the blood concentration of Ca2+ whenever it falls below some threshold value
• Raises blood calcium by:
  
  1. stimulating osteoclasts to release more Ca2+ from bone
  2. decreasing secretion of Ca2+ by the kidneys
  3. activating vitamin D which stimulates the uptake of Ca2+ by intestine
• Essential to life. W/o it would lead to lethal neuromuscular disorders

Question 46

Goiters

Answer 46

a swelling of the neck resulting from enlargement of the thyroid gland.

Question 47

Cortisol

(Glucocorticoids)

Answer 47

• Helps the body deal with stressful situations such as:
  
  • fasting
  • anxiety
  • trauma
  • crowding
  • and infection
• Keeps glucose levels high enough to support brain’s activities while forcing other cells to switch energy sources to amino acids and fats

Question 48

Aldosterone

(main mineralocorticoid)

Answer 48

• secreted by the zona glomerulosa in response to:
  
  • blood volume
  • blood pressure
• Released in severe hemmorhage

Question 49

Pineal Gland

Answer 49

• Small, pine cone shaped structure at the end of a short stalk on the roof of the diencephalon
• Produces melatonin

Question 50

Thymus

Answer 50

• In the lower neck, anterior thorax
• Thymic hormones
  
  • family of peptide molecules

Question 51

Gonads

Answer 51

• testes and ovaries
• main source of steroid sex hormones
• Testes produce androgens
  
  • primarily testosterone
    
    • maintains reproductive organs and promoted formation of sperm
• Ovaries produce
  
  • estrogen
    
    • maintain reproductive organs
  • progesterone
    
    • signals uterus to prepare for pregnancy

Question 52

Adrenal Cortex

Answer 52

• 3 layers
• secretes corticosteroids
  
  • ​mineralocorticoid
    
    • ​aldosterone
  • glucocorticoids
    
    • ​cortisol

Question 53

Adrenal Medulla

Answer 53

• secrete
  
  • epinephrine
  • norepinephrine

Question 54

Pancreas

Answer 54

• Secretes
  
  • Glucagon
    
    • liver cells release glucose from storage
  • Insulin
    
    • signals most cells to take up glucose from blood and to store glucose in liver to lower blood sugar levels
  • somatostatin
    
    • inhibits secretion of glucagon and insulin
  • pancreatic polypeptide
    
    • inhibits exocrine activity in pancreas