Endocrine System

Question 1

Basic Functions + Hormones

Answer 1

• part of the body’s regulatory system > works alongside nervous system
• endocrine: secrete hormones (chemical messengers) carries by blood to target organs
• exocrine: produce secretions (released via ducts and close to effector organs)
• hormones>steroids, proteins or amines>regulates activity of target organ, slow but long-lasting response
• glands= pituitary, thyroid, parathyroid, pancreas, ovaries, testes, adrenal
• respond to stimuli:
  nerve impulses adrenaline>adrenal medulla>nerves from sympathetic NS
  stimulating/releasing hormone thyroid-stimulating hormone (TSH)>anterior pituitary
  levels of certain chemicals raised blood glucose levels>insulin (pancreas)
  feedback loops ovaries>oestrogen stops FSH from anterior pituitary>prevent oversecretion/reduces secretion
  Some hormones from tissues:
• Gastrin>Stomach
• Secretin>Small Intestine
• Chorionic gonadotrophin>Ectodermal layer of the chorion in pregnancy
• Erythropoietin>Kidney

Question 2

Pancreas

Answer 2

• Lies in loop of duodenum ~ mixed gland:
  exocrine=digestive juices=pancreatic duct
  endocrine=Islets of Langerhans
  Islet of Langerhans secrete 3 hormones:
• Insulin (beta cells)>high blood glucose levels>inc. glucose uptake>stores excess glucose as glycogen (liver)
• Glucagon (alpha cells)>low blood glucose levels>breakdown glycogen stores in the liver
• Somatostatin (delta cells)>prevents wild fluctuations of blood glucose levels>dec. gut motility + secretion of digestive juices

Question 3

Pituitary Gland

Answer 3

• Ventral to hypothalamus
• AKA the hypophysis, divided into 2 lobes ~ “master” gland
  Anterior
  -adenohypophysis producing:
  TSH stimulates thyroid gland
  GH controls rate of growth (epiphyses of bones, protein production from AA, regulating use of energy)
  Adrenocorticotrophic Hormone (ACTH) stimulates adrenal cortex
  Prolactin stimulates development of mammary glands + secretion of milk
  FSH stimulates germ cells in the ovary to develop follicles
  LH stimulates ripe follicles to rupture and release ova
  Interstitial Cell Stimulating Hormone (ICSH) stimulates interstitial cells in testis to secrete testosterone
  Posterior
  Neurohypophysis (secreted and stored ~ hypothalamus and posterior pituitary gland)
  ADH alters permeability of collecting ducts in the kidney (water) > maintains homeostasis, response of ECF
  Oxytocin acts on mammary glands (milk released when young suckles) and causes contraction of uterus smooth muscle at gestation end (parturition and delivery)

Question 4

Thyroid Gland

Answer 4

• Midline of ventral aspect of trachea (first few rings)
• Controlled by TSH
• Secretes 3 hormones:
  1)Thyroxin (T4)
  2)Tri-iodothyronine (T3)
  Both have similar effects
  T3 = trace element of iodine (lacking> dramatic effect)
  Both affect uptake of O2, essential for normal growth
  3)Calcitonin
  Lowers blood calcium levels (dec. rate of bone resorption)
  High blood calcium > deposit in bone, reservoir for later

Question 5

Parathyroid Gland

Answer 5

• Either side of thyroid gland
• Secretes parathormone (dependent on calcium=blood levels)
• Oversecretion (hyperparathyroidism)
  Primary hyperparathyroidism:
  Due to neoplasia of parathyroid>causes bone resorption, bone weakness and pathological fractures
  Secondary hyperparathyroidism:
  Chronic renal failure>Ca2+:PO43- ration altered by impaired kidney function>inc. parathormone output, inc. bone resorption for maintenance of blood calcium levels>preferential resorption (mandible + maxilla)
  Nutritional hyperparathyroidism:
  Low Ca2+ diet>parathormone produced to raise calcium levels by bone resorption

Question 6

Ovary

Answer 6

• Either side of dorsal abdominal cavity, caudal to kidneys
  Oestrogen:
  Walls of developing ovarian follicles>causes behaviour associated with oestrus cycle, prepares reproductive tract + external genitalia>negative feedback (anterior pituitary) ~ no more FSH
  Progesterone:
  Corpus luteum (remaining follicular tissue)>develops from LH, prepares for pregnancy + maintains>negative feedback (hypothalamus) ~ no gonadotrophin RH>development of mammary glands>relaxin ~ ligaments soften around the birth canal

Question 7

Testis

Answer 7

• External to body cavity of the abdomen, within scrotum
  Testosterone:
  Produced by interstitial cells in response to ICSH from anterior pituitary>development of male characteristics (penis+barb penis development, muscle, jowls (tomcat) and size)>male behaviour patterns (sex drive, aggression, territorial + mating behaviour)>spermatozoa development
  Oestrogen:
  Small quantities by Sertoli cells, seminiferous tubules of testes

Question 8

Adrenal Gland

Answer 8

• Pair, close to cranial pole of each kidney
• Outer cortex, inner medulla

Cortex:
Hormones=Steroids
Glucocorticoids>regulated by ACTH from anterior pituitary = cortisol + corticosterone>inc. blood glucose levels, inc. conversion of AA to glucose (gluconeogenesis)>depress inflammatory reaction (delay healing/repair)
Mineralocorticoids
Aldosterone (distal convoluted tubule of kidney)>regulates acid-base balance (plasma, ECF) ~ excretion of Na+, K+, H+
Adrenal Sex Hormones
Secreted in significant quantities (some animals, though neutered, how certain level of sexual behaviour)

Medulla:
Controlled by sympathetic NS (fight or flight)
Adrenaline and noradrenaline
Raised blood glucose levels (breakdown of glycogen)
Inc. heart rate + rate/depth of respiration
Dilated blood vessels of skeletal muscles
Dec. activity of GI tract + bladder