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ENDO 207 FINAL > Physiology > Flashcards

Physiology Flashcards

1
Q

Describe the Mechanism of action of growth hormone?

A

1 GH binds 2 receptors → homodimer →activates JAK2 → autophosphorylation →

a. Phosphorylation of protein kinase C

b. Phosphorylation of insulin receptor substrate

c. Phosphorylation of (STAT) →↑protein synthesis

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2
Q

What are the effects of Growth Hormone on metabolism?

A
  1. On protein metabolism: anabolic →↑size & number of cells.
    a. ↑amino acid uptake
    b. ↑ DNA transcription
    c. Protein sparing: uses fatty acid for energy
  2. On carbohydrate metabolism: hyperglycemic
    a. ↓glucose uptake & utilization in skeletal and fat cells:
    b. ↑glucose production by the liver:
    * ↑ glycogenesis
  3. On fat metabolism: lipolytic & ketogenic
    a. ↑lipolysis →↑fatty acid (energy source)
    b. ↑ fatty acids uptake by the liver→ fatty liver & ↑ketone bodies formation
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3
Q
  1. Explain the effect of growth hormone on (bone and cartilage)?
A
  1. On bone and cartilage: GH stimulates growth at epiphysis indirectly via
    ➢ Stimulate release of Somatomedin by liver & Chondrocytes

Somatomedin C causes:
a. ↑division of chondrocytes
b. ↑protein deposition by chondrocyte
c. Differentiation of chondrocytes into osteogenic cells→ deposition of new bone.

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4
Q

What are Factors involved in regulation of GH Secretion/ describe role of hypothalamus?

A

GH increased by: GHRH, ↓blood glucose & FFA level, Fasting, Starvation, Exercise, Stress, Protein meal (arginine AA), sex hormones

GH decreased by: GHIH (Somatostatin), ↑blood glucose & FFA level
Obesity aging, Cortisol

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5
Q
  1. What are the main effects of prolactin?
A

Increase milk secretion
Prevent ovulation: inhibit gonadotrophic hormones effect on ovaries
Infertility & amenorrhea during lactation

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6
Q
  1. What are the main factors regulating prolactin Secretion?
A

1- Hypothalamus:
a. Prolactin stimulating hormone PRH.
b. Prolactin inhibiting hormone (dopamine) →inhibition of prolactin
c. Negative feedback: Prolactin →↑ dopamine secretion →↓ prolactin secretion

2- Physiological variations: factors ↑ PRL secretion
A. Pregnancy: ↑gradually & peaks at parturition.
B. Suckling: sharp rise with each nursing.
C. Sleep: ↑at onset then persists at plateau
D. Stress→↑ secretion

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7
Q
  1. Give an account on renal effects of Vasopressin (ADH)?
A

A – Renal effects:

  1. In tubular system:

a- Act on V2 receptors on principal cells in late DCT, collecting tubule →↑cAMP → translocation of aquaporin2 to cell membrane → ↑H2O permeability
b- ADH induces insertion of urea transporters (UT1) in medullary collecting duct →↑ flow of urea into medullary interstitium → ↑ osmolarity → ↑water reabsorption.

  1. In renal vascular system:
    * Act on V3 receptors in glomerular mesangial cells →↑ VD prostaglandin E2→ antagonizes VC effect of ADH→ maintains renal perfusion.
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8
Q

Mentions the extrarenal effects of Vasopressin (ADH)

A

B– Extra-renal effects:

  1. In vascular system: Act on V1 receptors →↑ Ca2+ influx → VC →↑ ABP in hemorrhage (minor effect) RAAS & Sympathetic nervous systems are the primary regulators of ABP.
  2. In stress: ADH & CRH are co-secreted from paraventricular nuclei→ stimulates corticotropes → ↑ACTH →↑cortisol
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9
Q

Explain how vasopressin (ADH) is regulated

A

ADH increase by: high plasma osmolarity which activates stretch inactivated cation channels which causes depolarization and ADH secretion. Low blood volume triggers atrial and baroreceptors which increase ADH. Nicotine. Stress

ADH decreased by: low plasma osmolarity, hypovolemia (low ECF), Alcohol, α- adrenergic agonists

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10
Q
  1. What are the effects of oxytocin?
A

Functions:

1- During sexual intercourse→ orgasm

➢In males: contraction of vas deferens → ejaculation.
➢In females: contraction of myometrium followed by relaxation →↓intra uterine pressure → help semen transport

2- During labor: contraction of the uterus

3- During suckling (Milk ejection): squeezing of milk from breast alveoli

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11
Q

How is oxytocin regulated?

A

Control: neurohormonal reflex

o Stimulus:
➢ Unconditioned: receptor stimulation (suckling, genital stimulation)
➢ Conditioned: higher center stimulation e.g. seeing, hearing, smelling or thinking.

o Efferent: hormonal→ release oxytocin from posterior pituitary

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12
Q

Describe the mechanism of action of thyroid hormone formation?

A

1- Thyroglobulin

2- Iodide trapping (pump): active (stimulated by TSH)

A. Na+ K+ pump →↓intracellular Na+
B. Co-transporter (2nd active transport) carries Na+ & I-
C. I- : is carried against electrochemical gradients
D. Iodide trapping also occurs in: mammary, salivary glands, gastric mucosa

3- Oxidation & Iodination: peroxidase oxidize (I-)→ iodine then binds iodine to thyroglobulin → MIT & DIT

4- Release of thyroid hormones: thyroid cells ingest part of thyroglobulin by pinocytosis→
* Pinocytic vesicles merge with lysosomes
* Proteinase →release T4, T3 ,DIT ,MIT from thyroglobulin
* De-iodinase removes (I) from DIT and MIT→ iodine is recycled again

5- Storage of thyroid hormones: extra amounts stored into follicle → cover any deficient intake for (2 – 3months) as

  • Iodide intake is variable
  • Thyroid cells contain small amount of reserve
  • Thyroid hormones are needed to be secreted daily in blood.
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13
Q

11.Describe the cellular mechanism of action of thyroid hormones?

A

Regulate gene expression:

a. T3 (mainly) & T4 bind to ligand binding domain of receptor.

b. Hormone –Receptor complex stimulate DNA transcription →formation of mRNA → translation in ribosomes →formation of many proteins.

These proteins either:
* Directly: induce cellular functions, or
* Indirectly: bind to new gene→ formation of new proteins → powerful cellular functions

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14
Q

12.Describe the effects of thyroid hormone on cell metabolic activity?

A

A-On mitochondria:

  • ↑size & number →↑ATP formation
  • Excessive ↑in thyroid hormones → mitochondrial swelling &↑ uncoupling of oxidative phosphorylation →smaller ↑in ATP & a greater loss of heat.

B- On ions transport: ↑ Na+ K+ ATPase activity →↑ Na & K transport & ↑energy consumption.

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15
Q

13.What are the effects of thyroid hormones on body metabolic processes?

A

A. On CHO metabolism:
* ↑glucose absorption, ↑insulin secretion, ↑glucose uptake by the cell,
* ↑ glycolysis & gluconeogenesis

B. On fat metabolism:
* ↑lipolysis→ ↑FFA oxidation
* ↓plasma cholesterol & ↑its secretion in bile via ↑LDL receptors on liver

C. On protein metabolism: anabolic

D. On BMR (40Calories / hr / m2 ) & normal body weight &appetite: necessary

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16
Q

14.Describe the effects of thyroid hormone on growth?

A

1.Mental growth & development of brain: in fetal & first few years of postnatal life→ induces neuronal, axonal & nerves ending formation.

  1. Skeletal growth
  2. Sexual growth: together with sex hormones
17
Q

15.Describe the effects of thyroid hormone on body systems?

A
  1. Primary effect: majority of systems are stimulated by a direct hormonal action.
  2. Secondary effect: many systems are stimulated by ↑metabolism (calorigenic action)

O2 consumption increase in CVS, Res, GIT
O2 consumption is decreased in anterior pituitary

18
Q

16.Give an account on Regulation of Thyroid function?

A
  1. Hypothalamus: TRH →bind G proteins on anterior
    pituitary thyrotropes→ activates PLC → ↑intracellular Ca2+ → ↑TSH release
  2. TSH: binds G proteins receptors on thyroid cells → activation of ACE →↑cAMP → activates kinase → phosphorylation in thyroid cells

A. Within 30 min: ↑proteolysis of thyroglobulin→↑T3 &T4 in blood.

B. Within hours, days, and weeks:
* ↑size, number, secretory activity of thyroid cells.
* Activation of iodide pump
* ↑ Iodination of tyrosine & formation of thyroid hormones.

  1. Feedback of thyroid hormones: ↑T3 &T4 →↓TSH by direct effect on hypothalamus →↓TRH
19
Q
  1. Compare between mechanism of action of Parathormone & vitamin D3?
A

Mechanism of action of PTH: PTH binds to Gs→ activates adenyl cyclase →↑cAMP

Mechanism of action of 1,25(OH)2D3: binds cytoplasmic receptor → hormone-receptor complex → stimulates DNA transcription → mRNA →formation of Calbindin D ( Ca2+ transport)

20
Q

18.Give an account on the physiological actions of PTH?

A

1-On Bone:

A- Rapid phase: “osteolysis” Start in min, continues for hours
* ↑ permeability of osteolytic membrane to Ca2+ from bone fluid.
* ↑intracellular Ca2+are pumped into ECF by Calcium pump.

B- Slow phase: days or weeks to develop
* PTH stimulates osteoblasts production of IL-6 and RANKL →stimulates osteoclasts proliferation
* Osteoclasts resorb both organic & inorganic bone →releasing, Ca2+, PO4– into ECF

2- On Kidneys
* ↓ PO4—reabsorption in PCT
* ↑Ca2+ reabsorption in DCT
* ↑Mg2++ reabsorption, ↓H+ secretion

3- On the intestine: →↑Ca2+ , phosphate absorption

21
Q

19.Give an account on the physiological actions of calcitonin?

A

A- On bones:

  • Stimulates osteoblasts
  • ↓number & activity of osteoclasts→ ↓ bone resorption
  • Inactivate Ca2+ pump of osteocyte

B- On kidneys: ↑ Ca2+ , PO4—excretion in urine

22
Q
  1. Give an account on the physiological actions of 1,25 – DHCC?
A

A- On intestine.

*↑calbindin D in intestinal epithelium→↑ Ca transports from brush to basal border
*Amount of Ca2+ absorbed α amount of calbindin D.
*Stimulates Ca2+ ATPase in basal border & alkaline phosphatase

B- On bones: depend on Ca2+ & PO4– concentrations:

*High Ca2+ & PO4–→ stimulates osteoblastic activity.
* Low Ca2+ & PO4– and under the effect of 1,25DHCC,

C- On kidney: ↑calbindin D→↑ Ca2+ absorption by DCT , ↑phosphates reabsorption by PCT

23
Q
  1. Factors regulating PTH
A

I- Regulation of PTH

1- Feedback of Plasma Ca2+: ↓plasma Ca2+ →↑ PTH secretion

2- ↑plasma PO4– →↓Ca2+ →↑PTH secretion
* PO4- also binds specific receptor in parathyroid gland →↑ PTH secretion.
* ↑PO4- →↑ (FGF23) →binds FGF-receptor in renal PCT →↓ PO4- reabsorption ‘

3- 1,25(OH)2D3→↓ PTH

4- ↑cAMP→↑PTH secretion.

24
Q

Factors regulating Vitamin D (1,25 DHCC)

A

II- Regulation of 1,25 DHCC

1- ↓ Plasma Ca2+ →↑ PTH → activate 1α hydroxylase→↑1, 25 DHCC

2- Feeds back of 1, 25 DHCC

  • 1, 25 -DHCC has –ve feeds back on 1alpha hydroxylase→ ↓formation of 1,25-DHCC.
  • 1, 25 -DHCC has +ve feeds back on convertase enzyme →↑24, 25 –DHCC (inactivation)
25
Q

Factors regulating of Calcitonin secretion

A

III- Regulation of Calcitonin Secretion:

  • ↑plasma Ca2+ →↓CT release
  • GIT hormones: gastrin, CCK →↑ calcitonin→ prevent post- prandial hyperecalcemia.
  • Beta adrenergic agonists, estrogen, prolactin, dopamine
26
Q
  1. What is meant by Permissive Action of Glucocorticoids/ list some of these actions?
A

Presence of small amount of cortisol is required for

1- Catecholamines, Angiotensin II → VC
2- Catecholamines, Growth hormone → lipolysis
3- Glucagon → glycogenolysis

ENDO 207 FINAL (4 decks)

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