chapter 13 endocrine system

Endocrine system

Regulates functions of the body to maintain homeostasis, and coordinates communication

Major endocrine glands

Pituitary gland, thyroid gland, parathyroid gland, adrenal glands, pancreas, pineal gland, thymus, ovaries and tested (reproductive glands)

Endocrine glands

Ductless; secrete hormones directly into the (blood) body fluids; everywhere in body. Hormones act only on target cells that contain receptors for them

Exocrine glands

Secrete into ducts that lead to a body surface. An example would be sweat glands.

Paracrine gland/secretions

Affect nearby/surrounding cells and structures

Autocrine gland/secretions

Affect only the cells that secrete them. Works in specific organ or gland that secretes them

Local hormones

Secrete locally

Differences between nervous and endocrine system

Nervous system: releases neurotransmitters and responds/reacts faster (touching a hot pan)

Endocrine system: secretes hormones and effects can last longer but are slower

Hormones

Organic compounds. Molecule that has a metabolic effect on another cell. Released into extra cellular fluid then diffuse into blood.

Has effect on some cells, not the other cells, because target cells have unique receptors for each hormone

Target cell

Cell has receptors for specific hormone

2 general types of hormones

Steroid or steroid like hormones & nonsteroid hormones

Steroid/steroid like hormones

Lipids containing complex rings of carbon and hydrogen atoms. All steroid hormones are produced from cholesterol.

• ex. sex hormones (testosterone, estrogens), adrenal cortex hormones (cortisol, aldosterone)

Nonsteroid hormones

Made from amino acids instead of cholesterol. Bind to receptors on the target cell membranes and is considered a first messenger. It triggers another chemical inside the cell called the second messenger, which causes the cells response.

• ex. Amines, proteins, peptides, glycoproteins

Signal transduction

The entire process of chemical communication, from outside cells to inside

Amines

Nonsteroid hormone that is derived from tyrosine (epinephrine, norepinephrine, thyroxine)

Proteins

Nonsteroid hormone composed of long chains of amino acids (growth hormone)

Peptides

Short chains of amino acids (ADH, oxytocin)

Glycoproteins

Nonsteroid hormone; carbs joined to proteins (TSH)

Upregulation

Hormone action that increases in number of receptors on target cells, in response to a decrease in hormone level

Downregulation

Hormone action that decreases in number of receptors on target cell, due to an increase in hormone level

What are steroids used for?

Used to increase muscular strength

What are growth hormones used for?

Used to enlarge muscles

What is erythropoietin used for?

Used to increase the # of RBC and oxygen delivery to muscles

Prostaglandins

Paracrine substances that promote inflammation and helps smooth muscles to contract. Controls movement of water and sodium

Hormone secretion and its effect

Secretion is primarily controlled by negative feedback (effect of hormone on its gland; to stop secretion) mechanisms. Effects can be short lived or may last for days (hormone has long half life)

3 methods of negative feedback control of hormones secretion

Hypothalamus: controls release of anterior pituitary hormones (tropic hormones: hormones that act on other glands to secrete hormones)

Nervous system control: NS directly stimulates some glands to secrete their hormones (via nerve impulses)

Changes in composition of internal environment: changing levels of a specific substance in the blood (an ion, glucose, etc) stimulates or inhibits secretion of certain hormones.

Positive feedback

Rising level of a hormone leads to an increase in secretion. Secrete more hormones

Pituitary gland

Lies at the base of the brain and is controlled by the brain, specifically the hypothalamus. Attached to hypothalamus by pituitary stalk (infundibulum).

2 distinct portions of pituitary gland

Anterior lobe (adenohypophysis) and posterior lobe (neurohypophysis). The secretion from these lobes are controlled by different methods by the hypothalamus.

How does the Hypothalamus control peripheral endocrine glands?

The hypothalamus releases releasing or release-inhibiting hormones that travel to the anterior pituitary gland.

These hormones target specific hormone-secreting cells in the anterior pituitary, causing them to release hormones that act on other endocrine glands.

Anterior pituitary hormones

Anterior lobe of pituitary gland that is produced in the anterior lobe, by 1 of 5 types of secretory cells

Major anterior pituitary hormones

Growth hormone (GH), prolactin (PRL), thyroid-stimulating hormone (TSH), adrenocorticotropic (ACTH), follicle-stimulating hormone (FSH), luteinizing hormone (LH)

Growth hormone (somatotropin) function

Stimulates cells to enlarge and divide rapidly, increases amino acid uptake and protein synthesis, decreases rate of carb usage, increases rate of fat usage.

GH secretion increases at puberty and off level in adolescence

Prolactin function

Promoted milk production in females

Thyroid-stimulating hormone (TSH) function

Stimulated secretion of thyroid hormones (T3 and T4) from thyroid gland

Adrenocorticotropic hormone (ACTH) function

Stimulates secretion of cortisol and other glucocorticoids from adrenal cortex

Follicle-stimulating hormone (FSH) function

Causes growth and development of ovarian follicles in females, sperm production in males

Luteinizing hormone (LH) function

Causes ovulation in females, sex hormone production in both genders

Hypopituitary dwarfism

Caused by deficiency of human growth hormone (HGH) during childhood.

Gigantism

Caused by oversecretion of GH during childhood

Acromegaly

Caused by oversecretion of GH during adulthood; no increase in height, but bone thickens

Where are the posterior pituitary hormones produced and released?

Produced in hypothalamus (neurosecretory cells) and stored and released by the posterior pituitary gland

Two hormones released by the posterior pituitary gland

Antidiuretic hormone (ADH, vasopressin) and oxytocin

What does Antidiuretic hormone (ADH) do?

Decreases urine production by reducing volume of H2O the kidneys excrete. Inhibited by alcohol consumption

• diabetes insipidus: insufficiency of ADH

What does oxytocin do during childbirth?

Causes muscle contractions in the uterine wall during childbirth

Thyroid gland

Lies just below the larynx, anterior and lateral to the trachea

What 3 hormones does the thyroid gland produce?

T4 (thyroxine): produced by follicular cells

T3 (triiodothyronine): produced by follicular cells

Calcitonin: produced by extra follicular cells

Disorders of thyroid gland: Hyperthyroid

Hyperthyroidism: sensitivity of heat, hyperactivity, weight loss, protruding eyes, goiter

Graves’ disease (autoimmune): mimicking action of TSH, exopthalmia (protrusion of the eyes)

Disorders of thyroid gland: Hypothyroid

Hashimoto disease (autoimmune): autoantibodies destroy thyroid cells, resulting in hypothyroidism

Hypothyroidism (infantile): cretinism deficiency in thyroid hormone at birth. stunted growth, intellectual disability

Hypothyroidism (adult): mental dullness, weight gain

Simple goiter: deficiency of thyroid hormones due to iodine deficiency.

What do Parathyroid Glands secrete and what controls the secretion?

They secrete 1 hormone, the parathyroid hormone. Blood calcium concentration controls the secretion of PTH

How is vitamin D activated and what is its function?

Activated by UV light in the skin, then processed in the liver and kidneys. It stimulates calcium absorption from the intestine.

Hyperparathyroidism

Overstimulates osteoclasts; too much bone breakdown (less bone density- can lead to fractures or osteoporosis). The cause is tumors.

Adrenal cortex

Outer portion of gland that secretes steroid hormones: Aldosterone, Cortisol, Sex hormones

Adrenal medulla

Central portion of the gland that increases BP, HR, and PR. Secretes amine hormones: 80% Epinephrine, 20% Norepinephrine (fight or flight)

Aldosterone

Conserves sodium and excretes potassium

Cortisol

Stimulated glucose synthesis from noncarbohydrates. Adrenocorticotropic hormone (ACH) from the anterior pituitary gland regulates the secretion

Adrenal androgens

Adrenocorticotropic hormone (ACTH) from the anterior pituitary plus unknown factors regulates the secretion

Addison disease

Hyposecretion of adrenal cortex hormones. Results in increased skin pigmentation

Cushing syndrome

Due to hypersecretion of cortisol

What kind of gland is the pancreas?

Endocrine & exocrine.

Endocrine function: secretes hormones into body fluids

Exocrine function: secretes digestive juices through pancreatic duct

3 hormones secreted from endocrine cells of Pancreas

Glucagon: increased blood glucose

Insulin: decreased blood glucose

Somatostatin: inhibits secretion of insulin and glucagon

Type 1 Diabetes Mellitus

Autoimmune disease; immune system destroys beta cells of pancreas. Lack of insulin production

Type 2 Diabetes Mellitus

Insensitivity of cells to insulin

Pineal gland

Secretes melatonin, which regulates circadian rhythms (day/night cycles) & exposure to light in night disrupt circadian rhythms

Thymus gland

Secretes thymosins, which promote development & differentiation of T-lymphocytes. Controls production of WBC’s

Stress causes BP to….

Increase