Hormone Regulation and Fluid Compartments

Hormone Regulation and the Endocrine System

• The endocrine system is a group of glands that regulate bodily functions through the release of hormones.
• Hormones are chemical messengers that travel through the bloodstream and act on target organs to control diverse bodily functions.
• Homeostasis is the physiological control of the body under stressful circumstances.
• The internal environment, outside of cells, is maintained relatively stable by the constant dynamic state of the extracellular fluids.
• Factors include the optimal concentration of gases, nutrients, ions, and water as well as optimal temperature and pressure.
• The endocrine system and the nervous system work together to coordinate body functions.

Fluid Compartments of the Body

• Total body mass varies slightly between males and females.
• 40-45% of total body mass in males/females is solids
• 60-55% of total body mass in males/females is fluids.
• 2/3 of total body fluid is intracellular fluid (inside cells)
• 1/3 of total body fluid is extracellular fluid (outside cells)
• Extracellular fluid is partitioned between plasma (20% of ECF) and interstitial fluid (80% of ECF).
• Interstitial fluid surrounds tissue cells and is connected to other extracellular fluids like cerebrospinal fluid and eye fluid.
• The distribution of fluid among these compartments is important for maintaining homeostasis.

Definitions

• Internal environment is the extracellular fluid compartment.
• Homeostasis is the relatively stable condition of the internal environment within the extracellular fluid.
• Homeostasis is a dynamic state of the extracellular fluid.
• Crucial for optimal concentration of gases, nutrients, ions, and water along with optimal temperatures and pressures.

How Homeostatic Mechanisms Maintain Body Health

• Homeostasis is maintained or restored through negative feedback.
• Negative feedback processes are important for normal body functioning and survival.
• Negative feedback processes are usually involved in self-regulation.
• Example: Increase in blood CO2 levels leads to an increase in breathing rate, which causes carbon dioxide concentration in the blood to return to homeostasis levels.

Homeostasis: Negative Feedback Loop

• Receptors detect imbalances (e.g. heat, cold).
• Afferent pathways carry information to the control center.
• The control center (thermoregulatory center in brain) processes the information.
• Efferent pathways deliver commands to effectors (sweat glands, muscles).
• Effectors produce responses (sweating, shivering) to restore balance.

What is a Gland?

• A gland is an organ that produces secretions.
• Secretions can include enzymes, hormones, etc.
• They are produced and secreted by specialized cells within the gland.
• Secretions can be secreted onto body surfaces (skin), into lumens of digestive organs, or into body tissues (including blood).
• Glands are either endocrine or exocrine.

Gland Types

• Exocrine glands discharge secretions into ducts leading to a specific target.
• Examples include sudoriferous glands (sweat), mammary glands (milk), salivary glands (enzymes), sebaceous glands (oil), and pancreatic enzymes.
• Endocrine glands release secretions (hormones) into interstitial fluid, which then enters the bloodstream and acts on distant target cells.
• Examples include pituitary gland, thyroid, adrenal glands, pancreatic islets, ovaries, testes, and placenta.

Hormones

• Hormones are chemical messengers produced by endocrine glands that travel through blood or lymph.
• Hormones regulate activity in one part of the body, in another.
• Each hormone has a specific receptor in the target organs.
• Hormones have variable structures (lipid or amino acid based)

Binding of Hormones

• Lipid-soluble hormones diffuse easily through the plasma membrane of target cells and bind to receptors inside the cytoplasm or nucleus.
• Water-soluble hormones bind to receptors on the plasma membrane, initiating intracellular signaling cascades.
• The speed of hormone action can be fast or slow, depending on whether it is water or lipid soluble.

Functions of Hormones

• Stimulate exocrine glands
• Stimulate other endocrine glands
• Affect growth and development
• Regulate metabolic processes
• Regulate muscle contraction, nervous stimulation
• Control reproductive processes

Endocrine and Nervous System

• The endocrine and nervous systems coordinate and integrate body cell activity.
• The endocrine system generates slower, longer-lasting responses as compared to the nervous system.
• Both are directed by the hypothalamus.

Endocrine Glands

• A list of glands and organs found in the endocrine system. Includes: pineal gland, hypothalamus, pituitary gland, thyroid gland, parathyroid glands, adrenal glands, pancreas, ovaries/testes (gonads), thymus, stomach, duodenum, and placenta(and other less understood ones).

Hypothalamus and Pituitary Gland

• The hypothalamus is a crucial link between the nervous and endocrine systems.
• It controls the release of hormones from the pituitary gland.
• The pituitary gland hangs down from the hypothalamus by a stalk called the infundibulum.
• The pituitary gland has two lobes: anterior and posterior, which have different functions and hormonal control pathways.

Hypothalamus and Anterior Pituitary

• Hypothalamic hormones travel through portal veins to the anterior pituitary to stimulate/inhibit hormone release.
• The anterior pituitary releases hormones into the secondary capillary plexus, then the general circulation.

Anterior Pituitary Hormones

• Six hormones are produced by the anterior pituitary: Growth Hormone, Thyroid Stimulating Hormone, Adrenocorticotropic Hormone, Follicle-Stimulating Hormone, Luteinizing Hormone, and Prolactin..

Anterior Pituitary Hormones details

• Table that describes Hypothalamus Hormones, Hormone released from the Anterior Pituitary, and Major function/target for each hormone
• Includes Gonadotropin releasing hormone, Prolactin releasing hormone and inhibiting hormone

The Hypothalamus and the Posterior Pituitary

• The hypothalamus produces two hormones: oxytocin and antidiuretic hormone (ADH).
• The posterior pituitary stores and releases these hormones.
• When stimulated, neurons in the hypothalamus release oxytocin and ADH into the posterior pituitary.

Hypothalamus and Posterior Pituitary details

• Table describing Hypothalamic neurons synthesizing oxytocin and ADH
• Oxytocin and ADH are transported down the axons to the posterior pituitary
• When stimulated, action potentials cause oxytocin or ADH to be released. Oxytocin and ADH effects are on target tissues.

Oxytocin

• Oxytocin targets smooth muscle in the uterus and breasts.
• In the uterus it stimulates uterine contractions, aiding in labor and delivery.
• After delivery, oxytocin is responsible for milk letdown in response to suckling from an infant.
• Involved in social bonding and maternal behavior

ADH = Antidiuretic Hormone

• ADH targets the collecting ducts in the kidneys to retain water.
• ADH targets sweat glands to minimize water loss.
• ADH causes arterioles to constrict, increasing blood pressure.

Thyroid Gland

• The butterfly-shaped thyroid gland is located inferior to the larynx and anterior to the trachea.
• It has two laterally placed lobes separated by a bridge-like isthmus.

Hormones of the Thyroid Gland

• Thyroid hormone (T3 and T4) is stimulated by thyroid-stimulating hormone (TSH), produced in the anterior pituitary.
• It is the major metabolic hormone of the body.
• It raises metabolic rate and affects tissue and development, and it impacts heart rate and blood pressure.
• Thyroid hormones are crucial for growth, development, and metabolism.

Disorders of Thyroid Hormone Secretion

• Hypersecretion causes Graves' disease, goiter, and increased metabolic rate.
• Hyposecretion can cause hypothyroidism.

Goiter and Low Iodine in Diet

• Goiter is an enlarged thyroid gland, often caused by low iodine levels in the diet or due to disorders in thyroid hormone production.
• The thyroid gland enlarges in an effort to produce more thyroid hormones.

Hormones of the Thyroid Gland (Calcitonin Details)

• Calcitonin lowers blood calcium levels by inhibiting osteoclasts (cells that break down bone) and stimulating osteoblasts (cells that form bone).
• It decreases calcium absorption in the intestines and increases the loss of calcium in urine.

Stop and Think Questions (Thyroid Gland)

• Various questions about the roles of various hormones (e.g. TSH)

Parathyroid Glands

• The parathyroid glands are small, round masses of tissue attached to the posterior surface of the lateral lobes of the thyroid gland; Usually two per lobe.

Parathyroid Hormones

• Parathyroid hormone (PTH) raises blood calcium levels, a crucial component of bone health, nerve, and muscle functions.
• It stimulates osteoclast activity, releases calcium from bone into the bloodstream, inhibits osteoblast activity.
• It enhances calcium reabsorption by the kidneys and promotes activation of Vitamin D, increasing calcium absorption in the intestine.

Regulation of Blood Calcium

• Low blood calcium levels trigger parathyroid hormone (PTH) release; PTH raises blood calcium by affecting bone, kidneys and intestines.
• High blood calcium levels trigger calcitonin release, which lowers blood calcium.

What if there is too much/too little parathyroid hormone

• Hyperparathyroidism: high blood calcium (hypercalcemia), impacts various bodily functions(bone issues).
• Hypoparathyroidism: Insufficient calcium that impacts the health of neurons and cells (spasms, convulsions).

The Pancreas

• The pancreas is both an endocrine and exocrine gland.
• Located posterior and inferior to the stomach.
• Most of the exocrine cells form clusters called acini and produce digestive enzymes.
• Endocrine tissue in the pancreas are in clusters called islets of Langerhans.
• Each pancreatic islet has four types of hormone-secreting cells: alpha, beta, delta, and F cells. Involved in the regulation of blood sugar.

Hormones of the Pancreas

• Alpha cells produce glucagon, increasing blood glucose levels. Crucial for maintaining glucose levels.
• Beta cells produce insulin, decreasing blood glucose levels. Crucial for maintaining glucose levels.
• These hormones work together in a delicate feedback system.

Carbohydrate Metabolism

• Glycogenesis is the formation of glycogen from glucose
• Glycogenolysis is the breakdown of glycogen to glucose
• Gluconeogenesis is the formation of glucose from noncarbohydrate sources (e.g., amino acids, glycerol)

Hormones of the Pancreas Details

• Hormonal control of blood glucose is complex, involving epinephrine, growth hormone, and cortisol, in addition to insulin and glucagon.
• Insulin and glucagon are counter-regulatory hormones that balance each other's effects on blood glucose.
• Detailed descriptions of the actions of these hormones on the body and how they regulate metabolism.

Glucose Homeostasis

• Blood glucose regulation through insulin and glucagon, and other hormones.
• Roles of the beta cells in insulin release, and alpha cells in glucagon release.
• Effects of the hormones on various body cells detailed.

When Things Go Wrong (Diabetes Mellitus)

• Diabetes mellitus occurs due to a loss of insulin or to cells that do not respond to insulin.
• Causes hyperglycemia and ketoacidosis.
• Two main types: Type 1 (juvenile) and Type 2 (mature onset)
• Symptoms and treatments are important.

Hormonal Control of Blood Glucose

• Table describing different endocrine glands, their stimulated action and the effects on blood glucose.

Thyroid Gland relationship to Blood Glucose

• Hypothyroidism leads to hypoglycemia, slowing down the metabolic process.
• Hyperthyroidism leads to hyperglycemia, increasing the metabolic process.

Stop and Think (Glucose metabolism)

• Question about which hormone isn't involved in glucose metabolism.

The Adrenal Glands

• Two adrenal glands, one superior to each kidney.
• Two distinct regions: cortex and medulla.
• Cortex secretes steroid hormones, including cortisol and aldosterone; also related to regulating sodium, potassium and water balance.
• Medulla secretes catecholamines, including epinephrine and norepinephrine. Involved with the fast-acting stress response.

The Adrenal Cortex

• The adrenal cortex is divided into three zones, each producing different steroid hormones:
  • Mineralocorticoids (aldosterone), regulates electrolytes in the blood.
  • Glucocorticoids (cortisol), regulates metabolism and stress response.
  • Cortical sex hormones (androgens and estrogens), support development and maintenance of secondary sex characteristics.

Mineralocorticoids: Aldosterone

• Aldosterone regulates Na+ and K+ concentrations in urine, sweat, and saliva.
• It regulates fluid and electrolyte balance by influencing reabsorption of sodium, which affects water reabsorption and impacts blood volume/pressure.

Glucocorticoids: Cortisol

• Cortisol regulates metabolism by promoting protein and fat breakdown to form glucose (gluconeogenesis)
• Raising blood glucose levels
• Helps the body cope with stress.

Cushing's Syndrome

• High levels of circulating cortisol (often caused by drug use or tumors).
• Manifests as hyperglycemia, poor wound healing, osteoporosis, dermatitis, moon face (facial features), buffalo hump (fat accumulation at the base of the neck), etc.

Addison's Disease

• Hyposecretion of glucocorticoids and aldosterone (often due to an autoimmune disorder).
• Symptoms include hypoglycemia, low blood pressure, dehydration, muscle weakness, weight loss, and electrolyte imbalances.

Testosterone and Estrogen

• Testosterone and estrogen are produced by glands and impact various aspects of growth and development.

Adrenal Medulla Hormones: Epinephrine and Norepinephrine

• Epinephrine and norepinephrine are produced in the adrenal medulla.
• They increase blood pressure, heart rate, breathing, blood glucose, and divert blood flow.

Stop and Think (Adrenal Gland)

• Question about the source of norepinephrine and epinephrine.

What is Stress?

• Stress is any stimulus that leads to an imbalance from homeostasis.
• Includes environmental physical stimuli and internal factors like pain, emotions, and psychological factors.

How Does the Body Deal with Stress?

• General Adaptation Syndrome (GAS) has three stages: Alarm phase, Resistance phase, and Exhaustion phase; response to stress.

Alarm Phase

• Hypothalamus activates autonomic nervous system to release epinephrine and norepinephrine from the adrenal medulla.
• Body responds with increased metabolic rate, respiratory and cardiovascular effects (increased heart rate, breathing, blood pressure).

Resistance Phase

• Hormones from the hypothalamus stimulate the anterior pituitary to release hormones (e.g., ACTH).
• These hormones stimulate the release of other hormones; body adapts and prepares to combat the stressor long-term; maintaining blood glucose levels and blood pressure.

Exhaustion Phase

• If the resistance phase fails, the body resources are depleted.
• Health problems may occur including low carbohydrate and fat stores, muscle loss, suppression of the immune system, ulcers, anxiety and depression.

Stop and Think (Stress response)

• Question about the what doesn't occur in the alarm phase while responding to a stressor

Ovaries: Estrogens and Progesterone

• Paired oval bodies in the female pelvic cavity.
• Stimulated by follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
• Produce estrogens and progesterone. Impacts development of female reproductive system and sex characteristics.
• Estrogens and progesterone have crucial roles in menstrual cycle, reproduction, and overall development.

Testes: Testosterone

• The male gonads (testes) are oval glands in the scrotum.
• Also stimulated by follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
• Produce testosterone, influencing primary and secondary sex characteristics and contributing to bone and muscle development.

Undercover Endocrine Organs

• Placenta regulates during reproduction.
• Stomach secretes gastrin to aid in digestion.
• Duodenum secretes secretin and cholecystokinin to regulate digestion.

Less Understood Endocrine Organs

• Thymus regulates immune system (development of T Cells), size decreases with age.
• Pineal gland secretes melatonin, affecting daily rhythms, and responding to light. (Important for regulating circadian rhythm and sleep.)

Prostaglandins

• Hormones found in most body cells. Made of lipids in the plasma membrane.
• Have various functions, such as influencing blood pressure, stomach secretions, immune responses , nerve impulses, and uterine contractions.