Endocrine System and Homeostasis

### The Endocrine System - Homeostasis

• The endocrine system is responsible for maintaining homeostasis, the balance of the body's internal environment.
• It works alongside the autonomic nervous system (ANS) to regulate internal processes.
• ANS is responsible for rapid changes, while the endocrine system manages slower changes.

### The Endocrine Glands

• The endocrine system is made up of ductless glands that secrete hormones directly into the bloodstream.
• The glands include:
  • Pituitary gland
  • Adrenal glands
  • Pancreatic islets
  • Pineal gland
  • Thyroid gland
  • Thymus
  • Parathyroid glands
  • Ovaries (female)
  • Testes (male)

Hormone Functions

• Hormones are chemical messengers that regulate various processes, including:
  • Growth and development
  • Stress response
  • Nutrition
  • Reproduction

### Disorders of the Endocrine System

• Disruptions in the endocrine system stem from hormone imbalances (too much or too little):
  • Hyper: Excess hormone production
  • Hypo: Deficient hormone production
• Examples:
  • Hypoglycemia: Low blood sugar
  • Hyperthyroidism: Excess thyroxine

### Clinical Importance

• Understanding the endocrine system is critical for:
  • Recognizing oral and clinical presentations of endocrine diseases
  • Managing medical emergencies related to endocrine disorders
  • Understanding patient behavior related to endocrine conditions

### Pituitary Gland and Hypothalamus

• Pituitary gland, located in the sphenoid bone, is connected to the hypothalamus via a stalk.
• Hypothalamus and pituitary gland operate as the negative feedback regulation system.

### Hypothalamus Hormones

• The hypothalamus secretes several hormones, including:
  • Growth hormone releasing hormone (GHRH)
  • Growth hormone release inhibiting hormone (GHIH)
  • Thyrotrophin releasing hormone (TRH)
  • Corticotrophin releasing hormone (CRH)
  • Prolactin releasing hormone (PRH)
  • Prolactin inhibiting hormone (PIH)
  • Luteinising releasing hormone (LHRH)
  • Gonadotrophin releasing hormone (GnRH)

### Pituitary Gland Hormones - Anterior Pituitary

• The anterior pituitary secretes:
  • Growth Hormone (GH): Promotes growth of various body parts (skeleton, muscles, connective tissues)
  • Prolactin: Stimulates lactation (milk production)
  • Thyroid Stimulating Hormone (TSH): Stimulates thyroid growth and activity
  • Adrenocorticotrophic Hormone (ACTH): Stimulates adrenal cortex activity
  • Gonadotrophins:
    • Follicle stimulating hormone (FSH)
    • Luteinising hormone (LH)

### Pituitary Gland Hormones - Posterior Pituitary

• The posterior pituitary secretes:
  • Oxytocin: Promotes uterine contractions and milk production
  • Antidiuretic Hormone (ADH, Vasopressin): Regulates water reabsorption by kidneys, influences blood pressure

### Thyroid Gland

• Situated in the neck, in front of the larynx and trachea.
• Secretes three hormones:
  • Thyroxine (T4)
  • Triiodothyronine (T3)
  • Calcitonin
• Iodine is essential for thyroid hormone production.

### Thyroid Hormone Functions (T4 & T3)

• Regulate:
  • Basal metabolic rate (energy expenditure)
  • Carbohydrate, protein and lipid metabolism (weight)
  • Female reproductive cycle and lactation
  • Nervous system
  • Cardiovascular system
  • Motility of the gastrointestinal tract (peristalsis)

### Calcitonin Function

• Regulates blood calcium levels by:
  • Reducing blood calcium levels
  • Storing calcium in bones
  • Excreting calcium via kidneys
• Calcitonin opposes the effects of parathormone.
• It is released in response to elevated blood calcium levels after meals.

### Parathyroid Glands

• Four small glands embedded in the thyroid gland (two per lobe).
• Produce parathormone (PTH), crucial for maintaining blood calcium levels.

### Parathormone Function

• Works with calcitonin to maintain blood calcium levels.
• Raises blood calcium by influencing:
  • Calcium absorption in the small intestine
  • Calcium reabsorption by the kidneys
• If dietary calcium is inadequate, PTH can stimulate calcium release from the skeletal system.

###  Importance of Calcium

• Calcium is essential for:
  • Muscle contraction
  • Nerve impulse transmission
  • Blood clotting

### Adrenal Glands

• Located atop each kidney, approximately 4cm long and 3cm wide.
• Composed of two parts:
  • Cortex (outer part): Essential for life
  • Medulla (inner part)

### Adrenal Gland Function

• Cortex: Produces:
  • Glucocorticoids: Regulate glucose metabolism (e.g., cortisol)
  • Mineralocorticoids: Regulate electrolyte balance (e.g., aldosterone)
  • Sex steroids: Influence sexual development (e.g., androgens)
• Medulla: Produces:
  • Catecholamines: Respond to stress (e.g., epinephrine, norepinephrine)

### Pancreatic Islets

• Clusters of cells within the pancreas that produce hormones.
• Secretes:
  • Insulin: Reduces blood glucose levels
  • Glucagon: Increases blood glucose levels
  • Somatostatin: Inhibits insulin and glucagon secretion

### Insulin Function

• Regulates blood glucose levels and other nutrients.
• Reduces blood glucose by:
  • Stimulating glucose uptake and utilization by muscle and connective tissues.
  • Promoting glucose storage by increasing glucose conversion into glycogen (primarily in the liver and skeletal muscles).

### Glucagon Function

• Increases blood glucose levels by:
  • Converting glycogen into glucose (glycogenolysis)
  • Stimulating gluconeogenesis (producing new glucose from sources like proteins)

### Hormones Secretion by Ovaries and Testes

• Ovaries (female):
  • Estrogen & Progesterone: Regulate the menstrual cycle, initiate sexual maturity
• Testes (male):
  • Testosterone: Produces spermatozoa, promotes sexual maturity, secondary sexual characteristics.

### Thymus Gland

• Located behind the sternum in the chest.
• Secretes Thymosin: essential for the development of T-lymphocytes for cell-mediated immunity.

### Thymosin Function

• Responsible for the growth and maturation of the thymus and other lymph tissues.
• Thymosin production declines with age, leading to a decrease in T-lymphocyte effectiveness.

### Pineal Gland

• Small gland (about 10mm long).
• Secretes Melatonin:
  • Contributes to the coordination of circadian rhythms (24-hour cycles)
  • May influence the hypothalamus.
  • Its secretion is suppressed by daylight.

Explore the crucial role of the endocrine system in maintaining homeostasis in the body. This quiz covers the main endocrine glands, their functions, and the disorders that arise from hormonal imbalances. Test your knowledge on how hormones regulate growth, reproduction, and stress responses.