Endocrine Physiology Quiz

Endocrine System Overview

• The endocrine system is a collection of glands that produce hormones.
• Hormones regulate metabolism, growth, development, tissue function, sexual function, reproduction, sleep, and mood.
• Hormones circulate throughout the body, affecting specific organs and tissues.
• The term "endocrine" comes from Greek words meaning "within" and "to secrete".

Endocrine System Objectives

• Define the endocrine system and its general function.
• Explain how the endocrine system maintains homeostasis.
• Explain the relationship between the endocrine system and the nervous system.
• Differentiate between endocrine and exocrine glands.
• Define hormones, their functions, and types.
• Describe ways to keep the endocrine system healthy.

General Function of Hormones

• Regulates extracellular fluid, metabolism, biological clock, contraction of cardiac and smooth muscle, glandular secretion, and some immune functions.
• Plays a role in growth and development, and reproduction.

General Function of the Endocrine System

• Receives support from other organs like kidneys, liver, heart, and gonads.
• These organs are secondary components of the endocrine system, performing endocrine functions.
• The kidney, for instance, secretes hormones such as erythropoietin and renin.

Types of Endocrine Glands

• Endocrine glands release hormones directly into the bloodstream (ductless).
• Exocrine glands release substances into ducts, either outside the body or into internal spaces (e.g., digestive glands, sweat glands).

Definition of Hormones

• Hormones are chemical messengers that act like messenger molecules in the body.
• Hormones are made in one part of the body.
• These messengers travel to other parts of the body and control how cells and organs function.

Important Functions of Hormones

• Growth and development (cell and tissue)
• Food metabolism
• Initiating and maintaining sexual development and reproduction
• Maintaining body temperature
• Controlling thirst
• Regulating mood and cognitive functioning

Types of Hormones (Classification)

• Classified by their proximity to the site of synthesis to their site of action (autocrine, paracrine, endocrine).
• Classified by their chemical structure (peptides/proteins, steroids).
• Classified by their solubility in aqueous (hydrophilic/liposoluble) medium.

Three Classes of Hormones

• Autocrine hormones act on the same cells that produce them.
• Paracrine hormones act on nearby cells.
• Endocrine hormones travel through the blood to target cells.

Four Classes of Hormones (Based on Chemical Structure)

• Peptides/proteins are made of amino acids joined by peptide bonds.
• Steroid hormones are made of fatty acids using cholesterol as a functional group.
• Amino acid derivatives
• Fatty acid derivatives

Two Classes of Hormones (Based on Solubility)

• Hydrophilic hormones (e.g., insulin, glucagon, and epinephrine) are soluble in water, and cannot cross the cell membrane.
• Lipophilic hormones (e.g., thyroid hormones and steroid hormones) are not soluble in water, but they can cross the cell membrane.

Control of Hormone Release

• Hormonal stimuli: Endocrine organs are activated by other hormones.
• Humoral stimuli: Changing blood levels of ions and nutrients.
• Neural stimuli: Nerve fibers stimulate hormone release.

Hormone Transport in Blood

• Hormones flow through the blood and bind to receptors within capillaries.
• Water-insoluble hormones bind to plasma proteins to be carried into the blood.
• Water-soluble hormones dissolve into the plasma.

Pituitary Gland

• The pituitary gland is a small, bean-shaped structure in the head.
• It receives signals from the hypothalamus and can release/inhibit hormones.
• The pituitary gland has two main lobes: anterior and posterior.
• The anterior pituitary produces and releases various hormones.
• The posterior pituitary releases hormones produced by the hypothalamus.

Anterior Pituitary Hormones

• Growth hormone (GH): Essential for growth and body composition. Important for children and adults, affects fat distribution and protein synthesis.
• Prolactin: Stimulates breast milk production after childbirth.
• Follicle-stimulating hormone (FSH): Works with LH to ensure normal function and development of the ovaries and testes, and the production of sperm and egg.
• Luteinizing hormone (LH): Works with FSH to ensure normal function of the ovaries and testes; triggers ovulation in females and stimulates testosterone production in males.
• Adrenocorticotropic hormone (ACTH): Stimulates the adrenal glands to produce hormones.
• Thyroid-stimulating hormone (TSH): Stimulates the thyroid gland to produce hormones.

Posterior Pituitary Hormones

• Antidiuretic hormone (ADH) (or Vasopressin): Maintains blood pressure, blood volume, and water content. Acts at kidney level on water reabsorption.
• Oxytocin: Involved in processes such as contracting the uterus during childbirth and stimulating breast milk production.

Pineal Gland

• The pineal gland is located in the back portion of the third cerebral ventricle of the brain.
• It is also known as the "pineal body".
• Its function is not fully understood, but it appears to play a role in regulating female reproduction, sexual maturation, circadian rhythms (such as sleep-wake cycles), and the body's internal clock.
• Pinealocytes produce and secrete melatonin; regulating female reproductive hormones, including menstruation.

Thyroid Gland

• The thyroid gland is located at the base of the throat.
• It is a large gland consisting of two lobes connected by an isthmus.
• The thyroid gland produces two main hormones: thyroxine (T4) and triiodothyronine (T3).
• It also produces calcitonin.
• T4 and T3 are produced from follicles and are essential for metabolic functions such as metabolism of energy sources (oxidation and conversion to chemical energy), and converting glucose into body heat.
• Calcitonin regulates calcium levels.

Parathyroid Gland

• The parathyroid glands are small glands located on the posterior aspect of the thyroid gland.
• The parathyroid glands release parathyroid hormone (PTH) in response to low blood calcium levels.
• PTH causes bone calcium release into the blood and stimulates calcium absorption in the kidneys and intestine.

Hypothalamus

• Part of the brain, located below the thalamus.
• It controls the pituitary gland's hormone secretion and regulates various body functions, including temperature maintenance, thirst, hunger, sleep, mood, and blood pressure.

Gonads

• The female (ovaries) and male (testes) gonads function as both exocrine (producing sex cells) and endocrine glands (producing sex hormones).
• Sex hormones produced by both the ovaries and testes are chemically identical, though the quantities vary between the two.

Ovaries

• The paired, almond-shaped ovaries are in the female pelvic cavity.
• Ovaries produce female sex cells (ova) and estrogen and progesterone.
• Estrogen promotes the development of secondary sexual characteristics and controls the menstrual cycle.
• Progesterone supports a pregnancy.

Testes

• The paired testes are located outside the female pelvic cavity in a sac called the scrotum.
• The testes produce sperm and testosterone.
• Testosterone promotes male secondary sexual characteristics and supports sperm production.

Adrenal Glands

• The adrenal glands are located on top of each kidney.
• They are composed of two parts: the adrenal medulla and the adrenal cortex.
• The adrenal cortex produces corticosteroids, such as mineralocorticoids (e.g., aldosterone) that regulate minerals and glucocorticoids (e.g., cortisol) that regulate glucose and help the body respond to stress.
• The adrenal medulla produces epinephrine and norepinephrine, part of the body's "fight or flight" response. These hormones enhance the body's reaction to an emergency.

Thymus Gland

• The thymus gland is located in the thoracic cavity, behind the sternum.
• It produces various thymosins and other hormones that regulate the maturation of T-cells, which are important for the immune system's function.

Kidney

• Kidneys produce renin, which helps regulate blood pressure.
• They produce erythropoietin, which stimulates red blood cell production.
• They produce calcitriol, which stimulates calcium absorption in the intestine.

Stomach and Intestine

• The stomach contains gastrin, which promotes the production of hydrochloric acid.
• The intestine contains secretin, which promotes the production of bicarbonate.

Other Endocrine Tissues & Organs

• Heart:
  • Produces atriopeptin (ANP)
• Adipose Tissues:
  • Produce leptin and resistin