Endocrine Ch.16 B

Oxytocin

• Regulated by Positive Feedback Mechanism

• Leads to increased intensity of uterine contractions, ending in birth

• Triggers milk ejection (let down reflex) in women producing milk

  • NOT related to milk production

Antidiuretic Hormone (ADH)

• ADH helps to avoid dehydration ow water overload

• Alcohol inhibits ADH release

Thyroid Gland

• Consists of two lateral lobes and connected by Isthmus

• Composed of follicles that produce Glycoprotein thyroglobulin

  • Colloid (thyroglobulin + Iodine)

• Other endocrine cells: Parafollicular cells produce Calcitonin

Thyroid Hormone

• Major metabolic Hormone

• Consists of two related Iodine- consisting compounds

  • T4= thyroxin(e), or Tetraiodothyronine

    • Makes up 90% of thyroid hormone

  • T3= Triiodothyronine

    • Makes up 10% of thyroid hormone secreted

Effects of thyroid Hormone

• Increasing metabolic rate

• Heat production (Calorigenic effect)

Thyroid Hormone Plays a role in…?

• Regulating tissue growth

• Maturation and reproductive capabilities

• Maintaining blood pressure

• Developing skeletal and nervous system

Synthesis of Thyroid Hormone

• Thyroglobulin: synthesized and discharged into the lumen

• Iodides are oxidized to iodine

• Iodine attaches to tyrosine, forming T1 and T2

  • Iodinated tyrosines link together to form T3 and T4

  • Colloid is then endocytosed

Transport and regulation of TH

• T3 and T4 bind to TBGs (Thyroxine- binding globulins) produced by the liver

• TRH can overcome the negative feedback mechanism

Endemic Goiter

• due to insufficient iodine, which cant make TH so no negative feedback occurs. More TRH and TSH are secreted.

Calcitonin

• A peptide hormone produced by parafollicular or C cells

  • Lowers blood calcium in children

  • Antagonist to the Parathyroid Hormone (PTH) and Calcitriol (activated vitamin D)

• Hydrophilic since its a peptide

• Inhibits osteoclast activity

• Regulated by Humoral and negative feedback mechanism

Parathyroid Glands

• Tiny glands embedded in the posterior aspect of the thyroid

• Chief (Principal) cells secrete PTH

• PTH (Parathormone, Parathyroid Hormone) regulates calcium in the blood

Effects of Parathyroid Hormone

• PTH release increases calcium in the blood

Adrenal (suprarenal) Glands

• Paired, pyramid shaped organs atop the kidneys

• Adrenal medulla: neural tissue that acts as part of the SNS

• Adrenal Cortex: Glandular Tissue

Adrenal Cortex

• Synthesizes and releases steroids hormones called Corticosteroids

  • Different corticosteroids are produced in each of the three layers:

    • Zona Glomerulosa- Mineralocorticoids (Aldosterone)

    • Zona Fasciculata- Glucocorticoids (Cortisol)

    • Zona Reticularis- Gonadocorticoids (Androgens)

Mineralocorticoids- Aldosterone

• Maintains sodium balance by reducing excretion of sodium from the body

• Stimulates reabsorption of sodium by the kidneys

• The salt retaining hormone

• Aldosterone secretion is stimulated by:

  • Rising blood levels of K+

  • Low blood Na+

  • Decreasing blood volume or pressure

The Four mechanisms of Aldosterone Secretion

• Renin-angiotensin mechanism

• Plasma concentration of sodium and potassium

• ACTH

• Atrial Natriuretic Peptide (ANP)- Inhibits activity of the zona glomerulosa

Glucocorticoids (Cortisol)

• Helps the body to resist stress by:

  • Keeping blood sugar levels relatively constant

  • Maintaining blood volume and preventing water shift into tissue

• Cortisol Provokes:

  • Gluconeogenesis (formation of glucose from noncarbohydrates)

  • Rises in blood glucose, fatty acids, and amino acids

Excessive Levels of Glucocorticoids

• Depress cartilage and bone formation

• Depress the Immune System

Gonadocorticoids (Sex Hormones)

• Androgens → Testosterone

  • Contribute to onset of puberty

  • Appearance of secondary sex characteristics

  • Sex drive in females

Adrenal Medulla

• Made up of Chromaffin Cells that secrete epinephrine and Norepinephrine

  • Secretion of these hormones causes the sympathetic response/ Fight or flight:

    • Blood glucose levels to rise

    • Blood Vessels to constrict

    • The heart to beat faster

    • Blood to be diverted to the brain, heart, and skeletal muscle

Stress Response GAS→ General Adaptation Syndrome

• Alarm reaction

• Stage of Resistance

• Stage of Exhaustion

Pancreas

• Pancreatic islets (islets of Langerhans) produce hormones:

  • Alpha cells → Glucagon

  • Beta Cells→ Insulin

Glucagon

• Polypeptide hormone that is hyperglycemic agent

• Its major target is the liver where it promotes:

  • Glycogenolysis: breakdown of glycogen to glucose

  • Gluconeogenesis: Synthesis of glucose from lactic acid and noncarbohydrates

  • Release of glucose to the blood from the liver

Insulin

• Lowers blood glucose levels

• Enhances transport of glucose into body cells

• Counters metabolic activity that would enhance blood glucose levels

Regulation of Blood Glucose Levels

• The hyperglycemic effects of glucagon

• The hypoglycemic effects of insulin

Diabetes Mellitus (DM)

• Polyuria- Huge urine output

• Polydipsia- Excessive Thirst

• Polyphagia- Excessive hunger and food consumption

• Hyperinsulinism- Excessive insulin secretion (or overdose), resulting in hypoglycemia

Gonads: Female

• Paired ovaries produce estrogens and progesterone

• Responsible for:

  • Maturation of the reproductive organs

  • Appearance f secondary sexual characteristics

  • Breast development and cyclic changes in the uterine mucosa

Gonads: Male

• Testes produce testosterone

• Testosterone:

  • Initiates maturation of male reproductive organs

  • Causes appearance of the secondary sexual characteristics and sex drive

  • Is necessary for sperm production

  • Maintains sex organs in their functional state

Pineal Gland

• Melatonin

  • Day/night cycles (Circadian rhythm)

  • Physiological processes that show rhythmic variations (body temp, sleep, appetite)

Thymus

• Essential for the development of the T lymphocytes (T cells) of the Immune system

Heart

• Produces atrial natriuretic peptide (ANP) which reduces blood pressure, blood volume, and blood sodium concentration

Gastrointestinal Tract

• Enteroendocrine cells release local acting digestive hormones

Placenta

• releases hormones that influence the course of pregnancy

Kidneys

• Secrete erythropoietin which signals the production of red blood cells

Skin

• Produces Cholecalciferol, the precursor of Vitamin D

Adipose Tissue

• Releases Leptin, which is involved in the sensation of satiety, and stimulates increased energy expenditure.