Physiology Block 3 Week 14 07 Intro to Pituitary Flashcards Preview

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Flashcards in Physiology Block 3 Week 14 07 Intro to Pituitary Deck (34)
1

Classic Hormone Groups

Tyrosine Derivatives
Steroids
Peptides/proteins

2

The class of hormone determines the mechanism of?

Synthesis and Secretion

Transport in the plasma compartment (protein binding)

Mechanisms and speed of onset of action (membrane receptors vs intracellular receptors)

Metabolism (half-life and metabolic clearance rate)

3

What are hormones?

Chemicals that are released through ductless glands and affect somewhere

4

Thyroid Hormones

% bound to plasma proteins
Half-life
Clearance

VERY high % binding to plasma proteins (99.95%)

Biologically active

VERY long half-lives
--Only free (dissolved) hormone can bind to receptor

LOW metabolic clearance

5

Steroid Hormones

% bound to plasma proteins
Half-life
Clearance

HIGH % binding to plasma proteins (94%)

LONG Half-life

Low Metabolic Clearance

6

Peptide and Protein Hormones

% bound to plasma proteins
Half-life
Clearance

ONLY circulate free form

SHORT Half-life

HIGH metabolic clearance

Exception = insulin-like growth factors

7

Endocrine Rhythms

Circadian
Ultradian
Stimulus-Induced
Seasonal

8

Circadian Endocrine Rhythm

Around the 24 hour clock

Test testosterone at morning when should be the highest

9

Ultradian Endocrine Rhythm

High frequency and Regular Bursts

Pulsatility of Luteinizing Hormone

10

Stimulus-Induced Endocrine Rhythm

Ex. Breast feeding is stimulus for increased prolactin

11

Seasonal Endocrine Rhythms

Ex. Vitamin D

12

Negative Feedback of Glucagon and Glucose

Glucagon is to prevent hypoglycemia

The alpha cells of the endocrine pancreas (produces glucagon) have glucose sensors that detect a decrease in EC glucose

-->increases glucagon release
-->stimulates hepatic gluconeogenesis and glycogenolysis
-->increased release of glucose form the liver restores blood glucose

Increased blood glucose inhibits alpha cells from producing glucagon

Parallel to Insulin

13

Negative Feedback of Insulin and Glucose

Insulin prevents hyperglycemia

An increase in blood glucose is sensed by the beta-cells of the endocrine pancreas

-->increases insulin release
-->insulin inhibits glucose release from the liver

Parallel to Glucagon

14

G-Protein Coupled Receptors Mechanism

Hormone activates the receptor

Inactive alpha, beta, and gamma G protein complex associates with the receptor and is activated
--exchanges GDP for GTP

Alpha unit dissociates and interacts with membrane-bound target proteins (Adenylyl cyclase)

Generation of second messengers!

15

G-Protein coupled generation of second messengers

FAST--Epi or ACTH

Cyclic adenosine monophasphate (cAMP) released in exchange for ATP

cAMP activates cAMP dependent Protein Kinase (PKA)

Phosphorylates proteins leading to a cellular response

16

G-Protein coupled to PLC, IP3, DAG second messenger system

Peptide hormone binds to receptor

Activates G-protein

Activates Phospholipase C

Splits PIP2 into DAG and IP3

IP3 exerts function on endoplasmic reticulum
-release of Ca2+ leads to cellular response
-release of inactive enzyme

DAG moves into cytoplasm and activates Protein Kinase C (PKC)

Phosphorylates inactive enzyme leading to cellular response

17

Lipophilic Hormones

SLOW--Cortisol

Steroids with intracellular receptors in target cells

Hormone binds to receptor in cytoplasm or in nucleus

Hormone-Receptor complex binds to hormone response element (promoter) on DNA
--Either activates or inhibits gene transcription, formation of mRNA, and protein synthesis

18

Mechanism of action of Thyroid Hormones

Nuclear Receptor

Thyroxine (T4) secreted from thyroid gland

Activated to T3 (by monodeiodinase) in cytosol and binds intracellular receptor, which binds promotoer
--allows a target tissue to regulate how much thyroid hormone action to which it is exposed

Ex. Heart can express the enzyme to convert T4 to T3

Ex. Inhibitors to prevent conversion as well

19

Pituitary Gland

Anterior Pituitary:
-Pars distalis
-Adenohypophysis

Pars Intermedia

Posterior Pituitary
-produces anti-diuretic hormone (vasopressin) and oxytocin


Hangs off base of brain by hypophysial stalk (infundibulum)

Neurons with cell bodies in the hypothalamus synthesize releasing or inhibitory (hypophysioTROPIC) factors and release them from short axons that terminate on capillaries in the median eminence

Forms portal veins that drain onto the anterior pituitary carrying hypophysiotropic factors

These factors stimulate or inhibit the release of anterior pituitary hormones that exit the pituitary via veins that drain into the petrosal sinuses and then jugular veins

20

Classes of Anterior Pituitary Hormones

Glycoproteins
Growth Hormone/Prolactin
POMC

21

Gylcoproteins

Anterior Pituitary Hormone

TSH, FSH, LH--stimulate synthesis

Identical alpha subunits
Beta subunit conveys receptor binding specificity

22

Growth Hormones/Prolactin

Anterior Pituitary Hormone

Promotes growth in stature and mass
Milk secretion

Amino Acid sequence homology

23

POMC

Anterior Pituitary Hormone

POMC gene produces a peptide (POMC) that is post-translationally modified to ACTH

Promotes synthesis and secretion of adrenal cortical hormones

24

Hypophysiotropic Hormones

Hypothalamic releasing or inhibiting hormones

Corticotropin Releasing Hormone
Gonadotropin Releasing Hormone
Growth Hormone Releasing Hormone
****Somatotropin Releasing-Inhibiting Factor (inhibits GH secretion)
Prolactin Stimulating Factor
***Prolactin Inhibiting Factor--Dopamine
Thyrotropin Releasing Hormone

25

Anterior Pituitary

Master gland

Controls:
-thyroid function (TSH)
-pre-pubertal growth
-adrenal cortex (ACTH)--release of adrenocortical hormones, gonadotropins (FSH and LH), and prolactin

26

Pituitary Descending Stimulation

Input to hypothalamus (environmental factors) increases or dec hypophysiotropic factor release

Hyopphysiotropic factor stimulates anterior pituitary to produce a tropic hormone

Stimulates a target gland to produce a final factor

27

Pituitary Control Feedback Loops

Long-Loop:
Target gland produces Target Gland Hormone
-serves as negative feedback on pituitary or hypothalamus

Ex. Cortisol increases and will shut off ACTH release

Short-Loop:
Pituitary hormone (tropic hormone) serves as negative feedback on hypothalamus

28

Trophic Effect

SLOW--growth effect over days and weeks

Nurturing/growth promoting effect

If ACTH high for a long time, stimulates adrenal growth and hypertrophy

If Low ACTH leads to adrenal atrophy

29

Tropic Effect

FAST--Immediate response

Acute stimulatory effects

ACTH stimulates cortisol release within minutes

30

Which of the following has the longest half-life?

Growth Hormone
Arginine Vasopressin
Testosterone
Angiotensin 2

Testosterone

Steroid Hormone, binds plasma protein

31

Want increase in Prolactin

Pregnancy, pituitary gets big, lots of prolactin produced

Dopamine inhibits prolactin--want to dec dopamine

Suckling inhibits the nerves in the hypothalamus that make dopamine
Dopamine goes down, releasing lactotroph, allowing prolactin to inc

32

Hypopituitarism

Too little pituitary function (anterior)

33

How do you treat a pituitary tumor?

Pituitary tumors express receptors for hyphysiotropic hormone that controls it

Give dopamine agonist--shrinks the tumor

34

Which of the following will lead to a decrease in prolactin secretion?

Dopamine Agonist
Dopamine Antagonist
Post-Partum Nursing
Pregnancy

Dopamine Agonist turns on dopamine, inhibiting lactotroph release of prolactin