Chapter 16 part 2) Endocrine system

Question 1

Thyroid Gland

Answer 1

• Butterfly shaped gland in anterior neck of the trachea
• Three parts
  
  • Isthmus) median mass connecting two lateral lobes
  • Follicles) hollow sphere of epithelial follicular cells
    
    • produce glycoprotein thyroglobuin
  • Colloid) Fluid of follicle lumin contains colloid (thyroglobin with iodine) which is a precourser to tyroid hormone
• Parafollicular cells produce calcitonin

Question 2

Thyroid hormone

Answer 2

• Major metabolic hormone in the body
• Two forms
  
  • T4 (tyroxine) major form that consists of two throsine molecules with four bound iodine atomr
  • T3 (Triiodotyronine) form that has two tyrosines with three bound iodine atoms
  • Both are amine hormones
• Effects of Thyroid hormone
  
  • Increases basal metabolic rate/ heat production (calorigenic effect)
  • Regulates tissue growth and development
  • Mantains blood pressure by increasing numbers of adrnergic receptors in blood vessels

Question 3

Synthesis of Thyroid Hormone

Answer 3

• Thyroid stores hromone extracellulary in follicle lumen untill triggered by TSH to release

1. Thyroglobin is synthesized and discharged into follicle lumen
2. Iodine is trapped; iodine ions (I-) are taken into the cell and released into the lumen
3. At the boarder of follicular cell and colloid, iodides are oxidized (electrons are removed and converted into normal iodine (I2))
4. Iodine is attached to tyrosine; mediated by preoxidase enzymes
   
   • Monoidotyrosine (MIT): one iodine attaches
   • Diiodtyrosine (DIT) two idoines attach
5. Iodinated Tyrosines link together to form T3 and T4
   
   • If one MIT(1) and one DIT(2) link, T3 is formed
   • If two DIT(2)’s combine, T4 is formed
6. Thyroglobin colloid is endocytosed by follicular cells
   
   • Vessicle is combined with a lysosome
7. Lysosomal enzymes cleave T3 and T4 from thryroglobin
   
   • Hormones are secreted in bloodstreams

• Mostly T4 is secreted (t3 is also)
• T4 must be converted to T3 at a cellular level.

Question 4

Transport and Regulation of TH

Answer 4

• T4 and T3 are transported by throxine-binding globulins (TBG’s)
  
  • Both bind to target receptors but T3 is ten times more active than T4
• Peripheral Tissues have an enzyme that converts T4 to T3
• TH release is stiulated by negative feeback
  
  • Falling TH levels stimulate releaze of Thyroid-Stimulating Hormone (TSH). Rising TH levels inhibit release of TSH
• Hypothalamlamic Thyroptopin-releasing hormone (TRH) can overcome negative feeback
  
  • occurs during pregnancy of when exposed to cold

Question 5

Myxedema

Answer 5

• Hyposecretion of TH in adults
• Symptoms
  
  • low metabolic rate, feeling chilled, constipation, thick and dry skin and puffy eyes, lethargy, edema, and mental sluggishness.
  • If due to the lack of iodine, a goiter (elarged thyroid) may develop.
• Usually casued by poor development of the thyroid gland.

Question 6

Graves Disease

Answer 6

• Due to hypersecretion of TH
• Autoimmune desiese) body will make antibodies that attach thyroid follicular cells. Antibodies mimic activity of TSH, which stimulates release of TH
• Symptoms
  
  • elevated metabolic rate, sweating, rapid and irregular heartbeats, nervousness, and weight loss despite adequate food
  • Expothalamos) protruding eyes due to tissue behind eyes expanding.

Question 7

Calcitonin

Answer 7

• Produced by parafollicular (C) cells in response to high Ca2+ levels
• Antagoist to Parathyroid Hormone (PTH). No known role in humans
  
  • has effects at higher-then normal doeses
  • Inhibits ostoblasts and release of Ca2+ from bone
  • Stimulated reuptake of Ca2+ from bone

Question 8

Parathyroid Glands

Answer 8

• Four to Eight tiny yellow-brown glands that are embedded in the posterior aspects of the thyroid. contain two types of cells
  
  • Oxyphil cells) unclear function
  • Parathyroid Cells) secreate Parathryroid hormone (PTH) or parathormone
• PTH is the most important hormone in Ca2+ homeostasis
  
  • secreted in response to low Ca2+ blood levels
• Funtions
  
  • Stimulate ostoclasts to digest bone and release Ca2+
  • Enhanses reabsorption of Ca2+ by kidneys and secretion of phospate (PO4)
  • Promotes activation of vitamin D which leads to increaed absorption of Ca2+ by the intestine.

Question 9

Homeostatic Imbalances of PTH

Answer 9

• Hyperparathyroidism) Due to parathyroid gland tumor
  
  • calcium leaches from bones, causing them to be soft
  • Elevated blood Ca depresses nervous system and helps form kidney stones
• Hypoparathyroidism) following glaund trauma or removal
  
  • causes hypocalcemia
  • results in tentany, respritory paralysis, and death

Question 10

Adrenal (Suprarenal) Glands

Answer 10

• Pared, Pyramid-shaped organs atop kidneys
• Structurally and Functionally it is two glands in one
  
  • Adrenal Cortex) three layers of glandular tissue that synthsize and secrete several different hormones
  • Adrenal Medulla) Nervous tissue that is part of the sympathetic nervous system.
• Adrenal cortex produces over 24 hormones collectively called corticosteriods
  
  • Sterioid hormones are not stored in cells. Rate of release depends on how fast synthesis is.
• Three layers of cortical cells produce diffrent corticosteriods
  
  • Zona Glomuerulosa) Mineralocorticoids
  • Zona Fasciculata) Glucocortioids
  • Zona Reticularis) Gonadocorticoids

Question 11

Mineralocorticoids

Answer 11

• Regulate elecrolyte concentrations in ECF
  
  • primarially Na+ and K+
  • Na+ affects ECF volume, blood volume, blood pressure and levels of other ions
  • Importance of K+) Sets resting membrane potenial of cells.

Question 12

Aldosterone

Answer 12

• The most potent mineralcoticoid
• Funtions
  
  • Stimulates Na+ reabsorption by kidneys
    
    • Results in increaded blood volume and blood pressue
  • Stimulates K+ elimination by kidneys
• Effects of alsoterone are short lived
  
  • Stimulates synthsis/ activation of Na+K+ATPase pumps.

Question 13

Mechanisms that Regulate Alosterone Setetion

Answer 13

• Renin-Angiotesin-Aldosterone Mechanism
  
  • Decreased blood pressures stimulates kidneys to release renin into blood
  • Renin cleaves off the plamsa membrane protien angiotensiogen and converts it into Angiotensin II
  • Angiotenisn II stimulates release of Aldosterone into blood.
• Plasma Concentration of K+
  
  • Increased levels of K+ directily influnce release of aldosterone
  • Low K+ levels inhibit release
• ACTH
  
  • Causes small increases of aldosterone during stress
• Atrial naturetic peptide (ANP)
  
  • secreated by the heart in response to high blood pressue.
  • blocks renin and alsoterone secretion to decrease blood pressure.

Question 14

Aldosteronism

Answer 14

• Hypersecretion of aldosterone due to adrenal tumors
• Results in:
  
  • Hypertensiona and edema due to excessive Na+
  • Excretion of K+ leading to abnormal nonresponsive nuerons and muscle.

Question 15

Glucocorticoiods

Answer 15

• Influence metabolism of most cells and help resist stressors
  
  • Keep blood gluscose levels constant.
  • mantain blood pressure through vasoconstrictor action
• Glucoorticoid hormones include
  
  • Cortisol (Hydrocortisone) only glucotorticoid in signifigent ammounts in humans
  • Cortisone
  • Coticosterone

Question 16

Regulation of Glucocorticoid (cortisol) Secretion

Answer 16

• Cortisol is Released in response to ACTH
  
  • ATCH is released in response to coricopin-releasing hormone (CRH)
  • CRH released in response to low cortisol levels.
  • Increased Cortisol levels inhibit ACTH and CRH through negative feedback.
• Corisol secretion cycles are governed by patterns of eating and sleeping
  
  • Levels peak after we rise in the morning
  • Lowest level just before we go to sleep.

Question 17

Cortisol

Answer 17

• Actions
  
  • Increase in blood levels of glucose, fatty acids, and amino acids.
  • Causes Gluconeogenisis: the formation of glucose from fats and proteins

Question 18

Gonadocorticoids

Answer 18

• Weak androgens (testosterone precursor) converted to testosterone in tissue cells
  
  • some is converted to estrogen
  • Ammount of testosterone is insignificant compared to that of the gonads.
• Hypersecretion of Gonadocorticoids
  
  • Results in Adrenogenital Syndrome (masculinization)
  • Not noticle in adult males
  • Prepubesent Boys) Reproductive organs mature
  • Females) beard, masculine body hair, clitoris resembeles small penis.

Question 19

Adrenal Medulla

Answer 19

• Medullary Chromaffin cells syntesize catecholamones
  
  • Epinephrine (80%)
  • Norepinephrine (20%)
• Effects of catcholamines
  
  • Vasoconstriction, Increased heart rate, Increased blood glucose levels
  • Blood diverted to brain, heart, and skeletal muscle
• Both hormones have same effects but
  
  • Epineprine) stimulares metabolic activities (Ex blood flow)
  • Norepineeprine) More influence on peripheral vasoconstriction
• Short Term Effects) Triggered by nerves from hypothalamus
• Long term effects) Triggered by hormone (ACTH) from anterior petuitary.
• Hyposecretion
  
  • No problems associated with hyposecretion
• Hypersecretion
  
  • Leads to symptone of uncontrolled sympathetic nervous system
  • Hyperglycemia, increased metabolic rate, rapid heartbeat, palpitations, hypertension, intense nervousness, and sweating

Question 20

Pineal Gland

Answer 20

• Small gland hanging from the roof of the third ventricle
• Pinealocytes secrete melatnin
  
  • derived from seration
• Melatonin may affect
  
  • Timing of sexual maturation and puberty
  • Day/night cycles
  • Physiological processes that show rhythmic variations (body temperature, sleep, appetite)
  • Production of antioxidant and detoxification molecules in cells

Question 21

Pancreas

Answer 21

• Triangular cells located partially behind stomach. Has both endo and exocrine cells
• Acinar Cells (Exocrone)
  
  • Produce enzyme-rich juice for digestion
• Pancreatic Islets (Islets of Langerhans) (Endocrine)
  
  • Alpha (α) cells) produce glucagon
  • Beta (β) cells) produce insulin (hypoglycemic hormone)

Question 22

Glucagon

Answer 22

• Triggered by decreased blood glucose levels and sympathetic nervous system
• Raised blood glucose levels by targeting the liver to
  
  • Break down glycogen into glucose (Glycogenolysis)
  • Synthesize glucose from latic acid/ other noncarbonates (Gluconeogenisis)
  • Release Gluscose into the blood

Question 23

Insulin

Answer 23

• Secreted when blood glucose levels increase
• Lowers blood glucose in three ways
  
  • Enhanses membreane transport of glucose into fat and muscle cells
  • Inhibits breakdown of glycogen into glusoce
  • Inhibits conversion of amino acids/ fats into glucose
• Plays a role in neroneal development, learning, and memory
• Insulin also triggers
  
  • Oxidation of glucose for ATP production
  • Polymerization of glucose to form glycogen
  • Convert glucsose to fat (adipose tissue)

Question 24

Factors that Influence Insulin Release

Answer 24

• Elevated blood glucose is primary stimulus for raised blood glucose.
• Raised blood levels for amino acids/ fatty acids
• Release of acetycholine by Parasympthetic nerve fibers
• Hyperglycemic Hormones (such as glucagon,epinephrine, growth hormone, thyroxine,glucocorticoids). All of these hormones increase blood glucose levels.
• Sympathetic nervous system inhibit insulin release

Question 25

Diabetes Mellitus (DM)

Answer 25

• Can be due to
  
  • Hyposecretion of insulin) type 1
  • Hypoactivity of insulin) type 2
• Three cardinal signs of DM
  
  • Polyuria) huge urine output
  • Polydipsia) excessive thrist
  • Polyphagia) excessive hunger and food consumption
• Ketones) Formed when fats are used as fuel insead of sugars
  
  • build up in blood can cause ketoacidosis (ph drops)
  • Hyperpnea) Rapid deep breathing

Question 26

Hyperinsulinism

Answer 26

• Excessive insulin secretion
• Causes hypoglycemia or low blood glucose levels
  
  • Symptoms: anxiety, nervousness, disorientation, unconsciousness, even death
  • Treatment: sugar ingestion

Question 27

The Gonads and Placenta

Answer 27

• The Ovaries produce estrogens and progesterone
  
  • Estrogen) matruration of reproductive organs, appearence of secondary sexual characteristics
  • Progesterone) causes breast development and menstral cycle
• Testes produce testosterone
  
  • Initiates maturation of male reproductive organs/ secondary sexual characteristics/ sex drice
  • Necessary for normal sperm production
• Placenta secrtes estrogens, progesterone, and human charionic gonadotropin (hCG)

Question 28

Hormone secretion by other organs

Answer 28

• Adipose Tissue (Fat) Secretes Leptin
  
  • apetite control; produces full felling
  • Ghrelin is the hunger hormone
• Gastrointestional Tract) Secrete digestive hormones
  
  • Ghrelin stimilates food intake
• Heart) Atrial natriuertic peptide
  
  • decreases blood Na+ concentration, blood pressure, and blood volume
• Kidneys
  
  • Erythropoitin) signals production of red blood cells
  • Renin) Initiates the renin-angiotensin-aldosterone mechanism
• Skeleton) Osteoblasts secrete ostocalcin
  
  • makes pancreas secrete more insulun
  • reduces body fat
• Skin) produces Cholecalciferol, the precursor of vitamin D
• Thymus) may be involved in normal development of T lymphocytes in immune response.

Question 29

Effect of Environmental Pollutants

Answer 29

• Exposure to pesticides, industrial chemicals, arsenic, and soil and water pollutants disrupts hormone function
  
  • Sex hormones, thyroid hormone, and glucocorticoids are vulnerable to the effects of pollutants
• Interference with glucocorticoids may help explain high cancer rates in certain areas

Question 30

Endocrine Function throughout life

Answer 30

• GH levles decline with age
  
  • mimics atrophy with age
• TH declines with age leading to lower metabolic rates
• PTH levels can decline in older women
• Glucose tolerance deteriorates with age
• Ovaries change significantly with age and can become unresponsive
• Testosterone also can diminsh with age but effect is not seen untill very old age.