Endocrine 2

Thyroid Gland Overview

Location

• Larynx

• Right lobe (Trachea)

• Left lobe

Hormones Produced

1. Thyroxine (T4): Major metabolic hormone

2. Calcitonin: Lowers blood calcium levels

Effects of Underactive Thyroid

• Disease Example: Myxoedema

• Symptoms:

  • Low metabolic rate

  • Weight gain

  • Feeling cold

  • Constipation

  • Lethargy

• Treatment: Iodine salts

Effects of Overactive Thyroid

• Disease Example: Graves' disease

• Symptoms:

  • Increased metabolic rate

  • Weight loss (despite high appetite)

  • Sweating

  • Protrusion of eyeballs

• Treatment: Surgery or medical treatment

Calcitonin Function

• Lowers blood calcium by:

  • Decreasing release of Ca from bones

  • Increasing uptake of Ca into bones

• Important during childhood for bone growth and remodeling

Thyroid Structure

• Composed of follicles that store thyroid hormones in a gelatinous mixture called colloid

Thyroid Hormones Effect

• Affects nearly all body's tissues except adult brain, testes, uterus, and thyroid itself

• Functions:

  • Stimulates breakdown of glucose

  • Increases metabolic rate

  • Increases heat production

Thermoregulation

• Core temperature: 37°C ± 0.5°C

• Heat Loss Mechanisms:

  • Radiation: Thermal waves (no contact)

  • Convection: Warm air rises, cool air replaces

  • Conduction: Heat through contact (e.g. getting into a bath)

  • Evaporation: Respiration (2%), skin/sweat (27%), mouth

Mechanisms Activated by Cold

• Shivering

• Increased hunger

• Increased secretion of hormones (thyroxine, adrenaline, noradrenaline)

• Increased metabolic rate

• Blood vessel constriction in skin

Growth Hormone Regulation

• Hypothalamic hormones involved:

  • Growth Hormone Releasing Hormone (GHRH)

  • Growth Hormone Inhibiting Hormone (GHIH)

Parathyroid Gland

• Location: Within the thyroid gland (usually 4 present)

• Chief Cells: Secrete Parathyroid Hormone (PTH)

Parathyroid Hormone (PTH) Functions

• Controls blood calcium levels:

  • Increases blood calcium if levels drop

  • Decreases PTH secretion if calcium levels are too high

• Actions:

  • Raises calcium in blood from bone matrix

  • Increases calcium reabsorption in kidneys

  • Increases intestinal calcium absorption

  • Activates Vitamin D in kidneys (vital for calcium absorption)

Conditions Related to PTH

• Hyperparathyroidism: Excessive PTH leads to calcium loss from bones, nervous system dysfunction, kidney stones.

• Hypoparathyroidism: Typically follows thyroidectomy, causing muscle twitches, untreated can lead to diaphragm dysfunction.