Endocrine System 4

Question 1

What are the layers and function of the adrenal cortex?

Answer 1

Zona glomerulosa- stimulated by angiotensin 2 and potassium to secrete aldosterone

Zona fasciulata- cortisol (controlled by ACTH)

Zona reticularis- androgens (controlled by ACTH)

LH has no effect on the production of adrenal androgens

Question 2

What are metabolic actions of cortisol?

Answer 2

Cortisol promotes metabolization of energy stores
Protein—> promotes degradation and increased delivery of hepatic gluconeogenesis precursors

1. Protein—> promotes degradation and increased delivery of hepatic gluconeogenesis precursors
2. Lipid—> promotes lypolysis and increased free fatty acids & glycerol
3. Carbohydrate—> increase hepatic output of glucose by inducing the enzymes involved in gluconeogenesis

Note: cortisol has permissive action which enhances the capacity of glucagon and Catecholamines (epine0hrine, norepinephrine )

Question 3

Summarize cortisol regulation

Answer 3

Corticotropin releasing hormone (CRH) secretion increases in response to stress and early morning

ACTH stimulate the secretion of cortisol (and andrenal androgens) of the adrenal cortex

Cortisol suppress the release of ACTH by acting on the hypothalamus and anterior pituitary

Question 4

Give all of aldosterone physiologic action

Answer 4

• luminal membrane contains sodium channels (ENaC). These channels allow for influx of sodium down its concentration gradient (created by Na+/k+-ATPase)
• Some chloride doesn’t follow sodium, creating a negative luminal potential causing potassium secretion
• Aldosterone activates the mineralocprticoid receptor on these cells, having he following effects:
  1. Increasing luminal ENaC effects

2. Increase ENaC opening time
3. Stimulates/Augments Na+/k+-ATPase

Luminal membrane contains a H+-ATPase, wh8ch pumps H+ into the lumen.

• Most of the H+ is eliminated from the body via buffers, phosphate and ammonia
• H+ pumped into the lumen binds to phosphate forming protonated phosphate, wh8ch is poorly reabsorbed, thus eliminating H+
• H+ can combine with ammonia to form ammonium, which is poorly reabsorbed and is thus excreted.

For every H+ excreted by the above buffers, bicarbonate is added to the body (new bicarbonate)

-Aldosterone stimulates H+-ATPase of intercalated cells. THUS, excess aldosterone causes metabolic alkalosis

Question 5

The major regulators of aldosterone are:

Answer 5

1. Angiotensin II
2. High potasssium (hyperkalemia)

Angiotensin II can be increased by any stimulus that causes renin release

1. Hypovolemia
2. Decrease sodium release to macula densa
3. Symparhetic(via B1 receptors) input to JGA cells

Question 6

Summarize the entire RAAS system

Answer 6

1. Dehydration,Na+ deficiency or hemorrhage
2. Decrease in blood volume
3. Decrease in blood pressure
4. JGA cells release renin
5. Angiotensinigen reacts with renin becomes angiotensin I
6. Angiotensin I converted to Angiotensin II in lungs by ACE
7. Angiotensin II causes vasoconstriction of arterioles which increases blood pressure increases until it returns to normal
8. Angiotensin II and hyperkalemia stimulate aldosterone release from the adrenal cortex
9. Kidneys increased Na+ and water Reabsorption and increased secretion of K+ and H+ ion urine
10. Increased blood volume leads to blood pressure increases until it returns to normal

Question 7

Describe type 1 diabetes

Answer 7

Lack of insulin

Increased secretion of glucagon, cortisol, growth hormone, Catecholamines

Increased catabolism, glycogenolysis gluconeogenesis(wasting), lypolysis (weight loss) increase- leads to hyperketoanemia leads to acidosis

Acidosis leads to hyperventilation(peripheral-hypotension)(vasoduartion- hypothermia)
Diabetic ketoacidosis leads to death

Lack of insulin leads to decreased anabolism leads to hyperglycemia (leads tofatigue and glycosuria), glycosuria(leads to Yulvitis Balantis and osmotic diuresis), osmotic diuresis leads to salt and water depletion. Salt and water depletion leads to tachycardia and hypotension and possibly death

Question 8

What are the adrenal androgens?

Answer 8

The major secreted form is dehydroepiandrostone (DHEA)

DHEA, DHEA sulphate and androstenedione have very low androgenic activity. They function primarily as precursors for the conversion to more potent testosterone and dihydrotestosterome

Question 9

Summarize the effects of the epinephrine

Answer 9

Liver—> promotes glycogenesis (break down glycogen to glucose). Increases glucose output by liver

Skeletal muscle—> pr9motes glycogenolysis but no glucose release (muscle lacks the enzyme to break it down all the way to glucose).

Adipose—> increase lipolysis, releasing glycerol, a substrate for gluconeogenesis

Question 10

What are the functions of delta cells in the pancreas?

Answer 10

Interspersed between alpha and beta cells. Constitute about 5% of islet cells

Question 11

What is the function of alpha cells?

Answer 11

Constitute about 20% of islet cells

Secrete glucagon and tend to be located near the periphery of the islet

Question 12

What are the functions of beta cells?

Answer 12

Beta cells constitute 60-75% of the islet cells.

Beta cells is synthesize preproinsulin, which is cleaved to form proinsulin, which, in turn, splits into insulin and C peptide- both of which are secreted in equilimolar quantities

Blood flows first to capillaries in the center of the islet and picks up insulin. Blood then flows to the periphery of the islets, where it acts on alpha cells to inhibit glucagon secretion.

C-peptide: long-term marker of endogenous insulin secretion

Question 13

Summarize control of insulin release

Answer 13

• Most of controller of insulin secretion is plasma glucose. Above a threshold of 100 mg, insulin secretion is directly proportional to plasma glucose
• Glucose enters the cell, causing a rise in intracellular ATP that closes ATP sensitive K+channels.
• Closureof the ATP-sensitive K+ channels results in depolarization causing voltage gated Ca2+ channel to open
• Rise in intracellular Ca2+ causes exocytosis of the vesicles containing insulin and C-peptide

Question 14

Summarize insulin effect of carbohydrate metabolism

Answer 14

• Insulin increases the uptake of glucose and its metabolism in muscle and fat
• Skeletal muscle and adipose tissue have GLUT-4 (glucose transporter)
• The rate of glucose transport in these two tissues is INCREASED by insulin which stimulates the movement of additional Glut-4 transporters to the membrane
• Insulin increases glycogen synthesis in the liver and muscle
• The activity of the enzyme that promote glycogen synthesis (Glucokinase & glycogen synthase) is increased

Question 15

Summarize protein metabolism of insulin

Answer 15

• Insulin increases amino acids uptake by muscle cells
• Insulin increases protein synthesis
• Insulin decreases protein breakdown (deficiency of insulin causes breakdown of protein)

Question 16

Summarize the actions of insulin lipid metabolism

Answer 16

• By increasing glucose uptake, insulin also promotes trios phosphate available for triglyceride synthesis
• Increases the activity of lipoprotein lipase. Lipoprotein lipase causes the release of free fatty acids from triglycerides
• Triglycerides synthesis (lipogenesis) is increased by insulin stimulating the Acetyl-CoA carboxylase

Question 17

Summarize the cellular action of insulin

Answer 17

Insulin promotes K+ movement into the cells. Although the overall action isn’t well understood, insulin increases the activity of Na/K+-ATPase in most body tissue.

NOTE: When a patient develops hyperkalemia (excess potassium in the blood), insulin and glucose is normally given to reduce the boood level of potassium

Question 18

What are the major actions of insulin?

Answer 18

Liver:
Increased -
-Glycogebesis 
-protein synthesis
-lipogenesis

Decreased-

• gluconeogenesis
• glycogenolysis
• Ketogenesis
• Ureagenesis

Muscle-
Increased-glycogenesis, protein synthesis, glucose oxidation

Decreased- glycogenolysis, proteolysis

Adipose
Increased lipogenesis
Decreased lipolysis

Question 19

Summarize pancreatic control of glucagon

Answer 19

• Low blood glucose (hypoglycemia) is the most important physiologic promoter for glucagon secretion and hyperglycemia is the most important inhibitor
• Amino acids especially dibasic amino acids such as arginine, also promotes the secretion of glucagon.

NOTE: Glucagon is secreted in response to the ingestion of a meal rich in protein

Question 20

What are the cellular actions of glucagon?

Answer 20

• Increase liver glycogenolysis
• Imcrease liver gluconeogenesis
• Increases liver ketogenesis and decrease lipogenesis
• increase ureagenesis
• increase insulin secretion
• increase lipolysis in the liver

Question 21

What are the relationship between insulin and glucagon?

Answer 21

Fed state: insulin dominates: anabolic

Increased glucagon oxidation, increased glycogen synthesis, increased fat synthesis, increased protein synthesis

Fasting state: glucagon dominates : catabolic

Increased glycogenolysis

Increased gluconeogenesis

Increased ketogenesis