Homeostasis 3.0

Endocrine Glands

A system of glands that release hormones directly into the bloodstream to regulate long-term body processes such as growth, metabolism, reproduction, and homeostasis

Hypothalamus

A region of the brain that links the nervous system to the endocrine system by producing hormones that control the pituitary gland; it uses neurons to send hormonal signals rather than nerve impulses

Pituitary Gland

Known as the “master gland,” this endocrine gland sits just below the brain and controls the activity of other endocrine glands through hormone release

Posterior Pituitary Lobe

The lobe of the pituitary that does not make its own hormones but stores and releases hormones produced by the hypothalamus, such as ADH and oxytocin

Anterior Pituitary Lobe

The lobe of the pituitary that produces its own hormones after receiving chemical signals from the hypothalamus and releases them to target organs

Antidiuretic Hormone (ADH)

A hormone released from the posterior pituitary that helps regulate water balance by increasing water reabsorption in the kidneys

Oxytocin

A hormone released from the posterior pituitary involved in childbirth contractions and social bonding behaviors

Thyroid Gland

An endocrine gland located in the front of the neck below the larynx, with two lobes on either side of the trachea, that regulates metabolism

Thyroxine (T4)

A thyroid hormone that increases the rate at which cells oxidize glucose and nutrients, raising overall metabolic rate

Triiodothyronine (T3)

A thyroid hormone that works with T4 to regulate metabolism and support growth and tissue development

Negative Feedback Loop (Metabolism)

A regulatory pathway where low metabolic rate triggers the hypothalamus to release TRH, stimulating TSH release from the pituitary, causing the thyroid to release T4 and increase metabolism

Calcitonin

A hormone released by the thyroid when blood calcium levels are high; it targets bones to promote calcium deposition and lower blood calcium levels

Goiter

An enlargement of the thyroid gland caused by iodine deficiency, leading to low thyroxine production and excessive TSH stimulation

Hyperthyroidism

A condition caused by excessive T4 production that results in symptoms like weight loss, heat intolerance, insomnia, high heart rate, and sometimes exophthalmos (bulging eyes)

Hypothyroidism

A condition where too little T4 is secreted, causing slowed metabolism, weight gain, cold intolerance, dry skin, and muscle weakness

Parathyroid Glands

Four small glands located near the thyroid that regulate calcium levels in the blood

Parathyroid Hormone (PTH)

A hormone released when blood calcium is low that targets bones, kidneys, and intestines to increase calcium levels in the bloodstream

Tetany

Muscle spasms of the hands and feet that can occur when parathyroid glands are damaged or removed, leading to dangerously low calcium levels

Growth Hormone (GH)

A hormone released by the anterior pituitary that stimulates protein synthesis, amino acid uptake, and bone elongation

Pineal Gland

A small gland near the center of the brain that secretes melatonin and helps regulate circadian rhythms based on light exposure

Melatonin

A hormone released during darkness that signals the hypothalamus to coordinate sleep-wake cycles and daily body rhythms

Digestive System

A continuous system from mouth to anus responsible for breaking down food and absorbing nutrients needed for energy, growth, and repair

Small Intestine

A long, folded tube (~6.7 m) where chemical digestion is completed and most nutrient absorption occurs through villi

Duodenum

The first section of the small intestine where bile, enzymes, and stomach acids mix to begin digestion and initial absorption

Jejunum

The middle portion of the small intestine that primarily absorbs carbohydrates, proteins, and increasing amounts of water

Ileum

The final section of the small intestine that absorbs fats, vitamin B12, and remaining water before waste enters the large intestine

Villi

Finger-like projections in the intestinal lining made of epithelial cells that increase surface area and release absorbed nutrients into the blood

Microvilli

Microscopic hair-like extensions on individual epithelial cells that further increase surface area for nutrient absorption

Large Intestine

A shorter (~1.5 m) organ that absorbs water and electrolytes, compacts stool, and stores waste before elimination

Cecum

The pouch connecting the small and large intestines where water and electrolyte absorption begins; the appendix is attached here

Ascending Colon

The part of the colon that removes water from stool, helping to harden it

Transverse Colon

The part of the colon where bacteria break down bilirubin and vitamins and water are absorbed

Descending Colon

The final storage area for stool before it moves to the rectum

Osmoregulation (Digestive System)

The regulation of water balance in the intestines using solute gradients and hormones like ADH and aldosterone

Mechanism of Water Absorption

A three-step process where Na⁺ and Cl⁻ are actively transported, creating an osmotic gradient that pulls water into intestinal cells and then into the bloodstream

Crohn’s Disease

An autoimmune inflammatory bowel disease that damages the intestinal lining, causing scar tissue and inflamed villi

Irritable Bowel Syndrome (IBS)

A disorder caused by disrupted brain–gut communication, leading to abnormal stool movement and food sensitivities

Sensory Receptors

Specialized cells that detect internal or external stimuli and convert them into nerve impulses for the brain to interpret

Mechanoreceptors

Receptors that detect mechanical energy such as pressure, movement, vibration, and body position

Photoreceptors

Receptors that detect light energy, allowing vision

Chemoreceptors

Receptors that detect chemical molecules or changes, such as taste, smell, and blood CO₂ levels

Thermoreceptors

Receptors in the skin that detect changes in temperature

Nociceptors

Pain receptors that detect tissue damage or harmful stimuli

Rods

Photoreceptors in the retina that detect brightness and shape and function best in dim light

Cones

Photoreceptors concentrated in the fovea that detect color and fine details in bright light

Cochlea

A fluid-filled structure in the inner ear where hair cells convert sound vibrations into nerve impulses

Semicircular Canals

Fluid-filled tubes in the inner ear that detect movement and help maintain balance

Taste Buds

Groups of chemoreceptors embedded in the tongue that detect sweet, sour, salty, bitter, and umami tastes

Olfactory Sense

The sense of smell, where airborne chemicals dissolve in nasal mucus and are detected by chemoreceptors that connect directly to the brain