Endocrine System Overview

Study Notes

Endocrine System Function

The endocrine system is a communication network within the body that helps regulate growth, development, reproduction, energy use, and electrolyte balance.
The nervous system is closely interconnected with the endocrine system to maintain homeostasis within the body.

Endocrine Glands and Hormone Production

Endocrine glands are specialized collections of cells that produce and secrete hormones.
Hormones are chemical messengers secreted directly into the bloodstream.
Adrenal Cortex: Produces cortisol and aldosterone.
- Cortisol increases glucose levels, suppresses inflammation and immune reactions.
- Aldosterone retains sodium and excretes potassium.
Intestine: Produces secretin and cholecystokinin.
- These hormones decrease gastric movement and stimulate bile and pancreatic juice secretion.
Kidney: Produces erythropoietin and renin.
- Erythropoietin increases red blood cell production.
- Renin increases blood pressure and vascular volume.
Ovaries: Produce estrogen and progesterone.
- These hormones promote secondary female sex characteristics and prepare the female body for pregnancy.
Pancreas (Islet of Langerhans): Produces insulin, glucagon, and somatostatin.
- These hormones regulate glucose and fat metabolism.
Parathyroid Gland: Produces parathyroid hormone.
- This hormone increases serum calcium levels.
Pineal Gland: Produces melatonin.
- Melatonin affects the secretion of hypothalamic hormones, specifically gonadotropin-releasing hormone.
Placenta: Produces estrogen and progesterone.
- These hormones facilitate fetal growth and development and prepare the body for delivery.
Stomach: Produces gastrin.
- Gastrin stimulates stomach acid production.
Testes: Produce testosterone.
- Testosterone promotes secondary male sex characteristics.
Thyroid: Produces thyroid hormone and calcitonin.
- Thyroid hormone stimulates the basal metabolic rate.
- Calcitonin decreases serum calcium levels.

Hormones

Hormones are chemicals produced in the body that meet specific criteria:
- Produced in small amounts
- Secreted directly into the bloodstream
- Influence normal metabolic cellular processes by reacting with specific receptor sites
- Rapidly broken down

Hypothalamus

The hypothalamus is the coordinating center for nervous and endocrine responses to internal and external stimuli.
It monitors the body's homeostasis by analyzing input from the periphery, the central nervous system, and coordinating responses through the autonomic, endocrine, and nervous systems.
The hypothalamus contains neurocenters that are sensitive to specific stimuli.
It regulates:
- Body temperature
- Thirst
- Hunger
- Water retention
- Blood pressure
- Respiration
- Reproduction
- Emotional reactions.
The hypothalamus receives input from the following:
- Limbic system
- Cerebral cortex
- Cranial nerves (smell, sight, touch, taste, hearing)
- Emotions and thoughts
The hypothalamus produces and secretes releasing hormones that stimulate the pituitary gland:
- Growth hormone
- Somatostatin (release-inhibiting factor)
- Prolactin (PRL)-inhibiting factor
The hypothalamus is connected to the pituitary gland by two networks:
- Vascular capillary network: carries hypothalamic hormones to the pituitary gland
- Nerve fiber network: transmits nerve impulses from the hypothalamus to the pituitary gland.