unit 8 notes Endocrine System Overview part 1

Definitions and Distinctions
- Endocrine Glands: Organs that secrete hormones directly into the bloodstream. Only endocrine glands belong to the endocrine system.
- Exocrine Glands: Glands that secrete substances through ducts to the external environment (e.g., sweat glands, salivary glands).

Definition: aHormones are chemical messengers produced by endocrine glands that travel through the bloodstream to target organs and tissues, regulating various physiological processes such as metabolism, growth, and mood. ` .

Endocrine System:
- Utilizes hormones for communication.
- Distributes hormones through the bloodstream.
- Responds slowly but has long-lasting effects.
- Adapts slowly to continual stimulation.
Nervous System:
- Uses neurotransmitters for communication.
- Secretes neurotransmitters into a synapse.
- Responds quickly with short-lived effects.
- Adapts quickly to continual stimulation.

General Functions: Hormones act as chemical messengers that control various physiological processes. They are generally slower and longer-lasting than neural impulses.

Nonsteroid Hormones (First Messengers):
- Bind to receptors on the target cell membrane, which triggers second messengers to modify the cell's activity.
Steroid Hormones:
- Typically bind to receptors within the target cell nucleus, influencing activity by acting on DNA. This is considered a slower process.
- Can also produce rapid effects when binding to surface receptors.

First Messenger: Nonsteroid hormones act as first messengers.
Process:
1. Hormone binds to a receptor on the cell membrane.
2. Activates G-proteins and adenylate cyclase.
3. Converts ATP to cyclic AMP (cAMP), the second messenger.
4. cAMP activates other enzymes to regulate cellular activity.

Process:
1. Steroid hormone passes through the plasma membrane.
2. Binds to a cytoplasmic receptor, forming a hormone-receptor complex.
3. Complex enters the nucleus, where it binds to DNA.
4. Activates transcription, leading to the production of new proteins that produce specific effects in the target cell.

Hormone secretion is controlled by homeostatic feedback mechanisms:
- Negative Feedback: Mechanisms that reverse changes in a physiological system. For example, elevated glucose levels trigger insulin secretion to lower glucose levels back to normal.
- Positive Feedback: Uncommon mechanisms that amplify physiological changes rather than reversing them, often related to childbirth.

Normal Glucose Level: Homeostasis restored via insulin secretion from the pancreas in response to high glucose levels.
Feedback Mechanism:
1. Intestines absorb glucose after a meal.
2. Glucose levels increase.
3. Pancreas secretes insulin to facilitate glucose uptake into tissues.

Definition: Prostaglandins (PGs) are tissue-specific hormones found in various body tissues.
Production: Often produced in local tissues and exert effects in those tissues.
Classes: Include prostaglandin A (PGA), prostaglandin E (PGE), and prostaglandin F (PGF).
Functions:
- Immunity: Mediating immune responses.
- Pain Control: Involved in pain signaling pathways.
- Respiration: Affecting airway dilation.
- Blood Pressure: Regulating vascular tone.
- Gastrointestinal Secretions and Reproduction: Influencing various reproductive processes.

Structure: Composed of two parts:
- Adenohypophysis (Anterior Pituitary)
- Neurohypophysis (Posterior Pituitary)

TSH (Thyroid-Stimulating Hormone): Stimulates the thyroid gland's growth and secretion.
ACTH (Adrenocorticotropic Hormone): Stimulates adrenal cortex growth and glucocorticoid secretion (primarily cortisol).
FSH (Follicle-Stimulating Hormone):
- Initiates ovarian follicle growth and ovulation.
- Stimulates estrogen secretion and sperm production in males.
LH (Luteinizing Hormone):
- Acts with FSH to stimulate follicle development and estrogen secretion.
- Causes ovulation and stimulates progesterone secretion.
- In males, stimulates testosterone secretion.
GH (Growth Hormone):
- Accelerates protein anabolism and fat catabolism.
- Slows glucose catabolism, increasing blood glucose levels (hyperglycemia).
PRL (Prolactin):
- Stimulates breast development during pregnancy.
- Promotes milk secretion postpartum.

ADH (Antidiuretic Hormone):
- Increases water reabsorption in kidney tubules, decreasing urine secretion.
Oxytocin (OT):
- Stimulates uterine contractions during labor.
- Facilitates milk ejection during breastfeeding.
- Enhances social bonding.

Role: Produces ADH and oxytocin, which are sent to the posterior pituitary.
Functions Controlled: Maintains homeostasis (temperature, appetite, thirst).
Integration: Connects with the nervous system for hormonal control.

Hormones:
- Thyroxine (T4): Increases metabolic rate.
- Triiodothyronine (T3): Similar function to T4, also crucial for metabolic processes.
- Calcitonin (CT): Lowers blood calcium levels by inhibiting bone breakdown.

Hormone: Parathyroid hormone (PTH)
- Function: Raises blood calcium levels by stimulating bone breakdown and mobilizing calcium from bones into the bloodstream.

High Blood Calcium Level: Triggers calcitonin secretion; decreases calcium levels by promoting deposition in bone.
Low Blood Calcium Level: Triggers PTH secretion; increases calcium levels by promoting bone resorpti on.

This unit covered the fundamental aspects of the endocrine system, including its glands, hormones, actions, and regulatory mechanisms essential for maintaining homeostasis in the body.
It highlighted the significant roles of the pituitary, thyroid, and parathyroid glands, among others, in physiological regulation.