Endocrinology Flashcards
Where is the pituitary gland located? How does it receive blood?
Pituitary gland sits in the bony fossa of the sphenoid bone in the brain - near to hypothalamus and optic chaism
It receives blood via the portal venous circulation from the hypothalamus
What hormones does the anterior pituitary secrete?
- Growth hormone, GH
- Thyroid stimulating hormones, TSH
- Adrenocorticotropic hormone (ACTH)
- Prolactin (PRL)
- Gonadal hormones, FSH, LH
What hormones does the posterior pituitary secrete?
Antidiuretic hormone (ADH, or vasopressin) Oxytocin
What is the Hypothalamic–pituitary–thyroid axis? (HPT)
Hypothalamus ↓ TRH (Thyrotropin-releasing hormone) ↓ Pituitary gland ↓ FSH (Follicle-stimulating hormone ) ↓ Thyroid - produces T3 AND T4 = -ve feedback on hypothalamus and pituitary
What hormones does the hypothalamus secrete?
- GHRH & SMS
- GnRH
- CRH
- TRH
- Dopamine
What controls prolactin, from where, what does it do
- Prolactin (PRL) is under -ve control by dopamine
- Causes milk production during lactation
- Produced by ant. pit.
How may a pituitary tumour present? (3)
- Pressure on local structure - eg, optic nerve
could cause headaches, hydrocephalus, damage to visual fields- (bitemporal homonymous hemianopia- damage to optic chiasm) CN damage - Pressure on normal pituitary
eg, hypopituitarism = pale, no body hair, central obesity - Functioning tumour
- prolactinoma (produces lactin = periods stop, infertile)
- acromegaly = thick skin, sweaty, greasy,
- crushing syndrome - increase steroids, cotisol = short and fat
What is the hypothalamic–pituitary–gonadal axis? (in females)
Hypothalamus ↓ GnRH ↓ Pituitary gland ↓ FSH and LH ↓ Oestrogen and progesterone
What is the hypothalamic–pituitary–gonadal axis? (in males)
Hypothalamus ↓ GnRH ↓ Pituitary gland ↓ FSH and LH ↓ LH acts on leydig = testosterone (-ve) FSH acts on sertoli = inhibin (-ve)
What is the hypothalamic–pituitary–adrenal axis?
Hypothalamus ↓ CRH (Corticotropin-releasing hormone) ↓ Pituitary gland ↓ ACTH (Adrenocorticotropic hormone ) ↓ Adrenal glands ↓ Cortisol (decreased immune system, breakdown of glucogen, proteins and fats) -VE FEEDBACK TO BOTH
*RESPONSE TO STRESS = SYMPATHETIC
Where is the pancreas located?
- Retroperitoneum
- Posterior to greater curvature of stomach
- Near C portion of duodenum
- small ducts then 2 larger ducts
Which cells associate with the exocrine function of the pancreas?
*exocine = glands that secrete their products through ducts opening onto an epithelium rather than directly into the bloodstream
pancreatic duct joins bile duct to form major duodenal papilla = into duodenum
Formed of small clusters of glandular
epithelial cells = Acini cells (98%)
manufacture and secretion of fluid and digestive enzymes - pancreatic juice - released into gut
Which cells associate with the endocrine function of the pancreas?
Islet cells (2-3%) Manufacture and release of several peptide hormones into portal vein
What is the effect of insulin?
- Reduces glucose output by the liver
- Increases storage of glucose, fatty acids and amino caids
(decreases glycogenolysis
decrease glucaneogensis = generation of glucose)
What is the effect of glucagon?
Glucagon mobilises glucose, fatty acids and amino acids from stores
(increases glycogenolysis
increase gluconeogenesis)
stimulated by low glucose levels
What is gluconeogenesis?
non-hexose substrates such as amino acids are converted to glucose (increase glucose)
What is glycogenolysis?
Glycogenolysis is the biochemical breakdown of glycogen to glucose (increase glucose)
What is glycogenesis>?
glycogenesis is the opposite, the formation of glycogen from glucose (decrease glucose)
How does the pancreas form embryologically?
At junction of foregut and midgut 2 pancreatic
buds (dorsal and ventral) are generated and
eventually fuse to form pancreas
Describe the microanatomy of Islet cells
-beta cell secretes insulin (proinsulin, then converted)
-alpha cell secretes glucagon
There is a paracrine ‘cross stalk’ between alpha and beta cells (ie local insulin increase, decrease glucagon)
How does somatostatin effect pancreatic hormones?
Suppresses the release of pancreatic hormones
Inhibits insulin release when somatostatin is released from delta cells of pancreas
Inhibits the release of glucagon
(secreted by delta cells)
Describe insulin secretion by beta cells
- Glucose enters cell via GLUT2 glucose transporter
- Glucokinase converts ADP to ATP
- K+ channel closes and depolarises membrane
- Ca2+ channel opens and causing Ca influx
- Ca activates insulin gene expression via CREB
(insulin acts on muscle and fats cells to reduce glucose conc)
Describe insulin action in muscle and fat cells
- Insulin binds to receptors on plasma membrane
- Intracellular signalling cascade
- GLUT4 vesicle mobilization to plasma membrane
- GLUT4 vesicle integration into plasma membrane
- Glucose uptake via GLU4
- Glucosa converted to glycogen
How do Bcells react the rising glucose?
- B cells sense rising glucose and aim to metabolise it
- First phase response is rapid release of stored product
- Second phase response is slower as it is the release of newly synthesised hormones