HUMB C10

Chemical Communication Methods

Autocrine

Paracrine

Neurotransmitter

Endocrine

Characteristics of Endocrine System

regulation requires duration, not speed

Glands secrete chemical messengers (hormones) into circulatory system

(blood)

Target cells respond to a hormone because they have the correct receptor

Hormone characteristics

Produced in small quantities

Transported in circulatory system

Act on target tissues elsewhere in body

Types of hormone secretion

Acute - sudden release due to stimulus, e.g. adrenaline in response to stress

Chronic - small variations over long periods, e.g. thyroid hormones

Episodic - e.g. estrogen & progesterone during menstrual cycle

Functions of the Endocrine System

Metabolism

Controls food intake and digestion

Tissue maturation

Ion regulation

Water balance

Heart rate and blood pressure regulation

Controls reproductive functions (gametogenesis and pregnancy)

Immune system regulation

Endocrine glands

(superior to inferior)

Pineal gland - circadium rythym

Hypothalamus - makes key hormones, regulates anterior pituitary

Pituitary gland - makes tropic hormones

Parathyroid glands - bone metabolism

Thyroid gland - stress, growth

Thymus gland - immune system, changes with puberty

Adrenal glands - cortex produces cortisol, medulla produces adrenaline

Pancreas - sugar metabolism

Gonads (ovary and testis) - produce hormones, sperm

Nervous vs Endocrine Systems - Similarities

Associated with brain via link between hypothalamus and pituitary gland

May use same chemical messenger as neutrotrasmitter and hormone

Cooperative - some parts of ES directly innervated by NS

Nervous vs Endocrine Systems - Differences

Mode of transport (axon vs blood)

Response speed (ms vs s)

Response duration (ms/s vs min/day)

Pituitary Gland Structure

Sits on inferior side of brain below hypothalamus

Posterior pituitary (neurohypophysis): extension of hypothalamus via infundibulum, secretes neuropeptides, developed by downward growth of nervous tissue during gestation

Anterior pituitary (adenohypophysis): secretes traditional hormones, developed by upward growth of oral cavity (glandular tissue) during gestation

Pituitary Gland - Hormone production

Produce 9 hormones (7 by anterior, 2 by posterior) that regulate body functions and the secretions of other endocrine glands

Hypothalamic control of Posterior Pituitary

Hormones produced and released by hypothalamic neurons then stored in posterior pituitary

axons form hypothalamohypophysial tract that runs down the infudibulum to connect hypothalamus to posterior pituitary

Hypothalamic control of Anterior Pituitary

Blood vessels make up hypothalamohypophysial portal system that connects hypothalamus to anterior pituitary

Hypothalamic neurons make releasing/inhibiting hormones that stimulate/inhibit anterior pituitary from releasing its own corresponding hormone

Hypothalamus, Anterior Pituitary, and Target Tissues

Stimuli in nervous system regulates secretion of releasing hormones from hypothalamic neurons

Releasing hormones go to anterior pituitary to stimuate the release of hormones

Hormones travel in blood to target tissue, which may be another endocrine gland

Anterior Pituitary Hormones

Growth hormone (GH): overall metabolism and growth

Thyroid stimulating hormone (TSH): Stimulates thyroid to secrete T3 and T4

Adrenocorticotropic hormone (ACTH): Stimulates adrenal cortex to secrete cortisol, androgens, and aldosterone

Melanocyte-stimulating hormone (MSH): Causes melanocytes to produce more melanin

Luteinizing hormone (LH) and Follicle-stimulating hormone (FSH) regulate production of gametes (sperm, oocytes) and reproductive hormones (testosterone, estrogen, progesterone)

Prolactin for milk production (lactation)

Tropic vs Non tropic Hormones

Tropic: stimulate the secretion of other hormones from target tissues

Non tropic: initiate an effect

GH is both

Most anterior pituitary hormones are tropic

Hypothalamus, Posterior Pituitary, and Target Tissues

Stimuli within nervous system cause hypothalamic neurons to increase or decrease action potential frequency

AP’s travel from hypothalamic neurons to posterior pituitary

Axon terminals of neurons in posterior pituitary store neurohormones that are released into circulatory system by AP’s to go to target tissue

Posterior Pituitary hormones

Both non-tropic

Antidiuretic hormone (ADH): When BP decreases, it stimulates increased reabsorption of sodium and water from nephrons so less urine is produced

Oxytocin: Uterine contractions during birth, milk ejection from lactating breast

negative feedback

Stimulus causes anterior pituitary to secrete a tropic hormone which travels in blood to target endocrine cell

Non-tropic hormone from target endocrine cell travels to its target to maintain homeostasis

Negative feedback produced that has opposite effect on hypothalamus and anterior pituitary to decrease secretion of tropic hormone

Positive feedback

Stimulus cause anterior pituitary secretes a tropic hormone which travels in blood to target endocrine cell

Non tropic hormone from target endocrine cell travels to its target

Positive feedback effect on hypothalamus and anterior pituitary increases secretion of tropic hormone

Cycle continues until stimulus is removed

Growth Hormone (GH)

Released by anterior pituitary when stimulated by growth hormone-releasing hormone (GHRH) from hypothalamus

Stimulates uptake of amino acids for protein synthesis and breakdown of fats to be used as energy

Promotes bone and cartilage growth

Regulates blood levels of nutrients after eating

Stimulates liver and skeletal muscle to make IGF-1 (non tropic effect)

Peak GH level during deep sleep

Uses negative feedback

Thyroid Stimulating Hormone (TSH)

Released from anterior pituitary when stimulated by thyroid-releasing hormone (TRH) from hypothalamus

Stimulates thyroid gland to release T3 and T4

Increases metabolism, body temp, and normal growth/development

Uses negative feedback loop

Thyroid Gland

One of largest endocrine glands

Highly vascular

Stores hormones in follicles

Increases metabolism in many tissues which increases body temp and essential for normal tissue growth

Adrenal gland

Loctaed at superior poles of kidneys

Medulla and cortex

Adrenocorticotrophic hormone (ACTH)

released by anterior pituitary when stimulated by corticotropin-releasing hormone (CRH) from hypothalamus

causes adrenal cortex to secrete:

cortisol (a glucocorticoid) - suppresses non-essential functions and raises blood pressure and glucose

aldosterone (a mineralocorticoid) - regulates salt, water, and blood pressure

Adrenal Medulla

Stress, physical activity, and low blood glucose stimulate hypothalamus to increase frequency of AP conducted through sympathetic nervous system

This stimulates adrenal medulla to secrete epinephrine (adrenaline) and norepinephrine (noadrenaline), which cause fight or flight responses

Melanocyte stimulating hormone (MSH)

Released from anterior pituitary by MRH and sunlight from hypothalamus

MSH causes skin cells to release melanin (colour pigment), as well as influencing appetite and sexual behaviour

LH & FSH

Gonadotropins: promote gonad growth and function

Released from anterior pituitary by GnRH from hypothalamus

Cause testes to make testosterone and sperm

Cause ovaries to make estrogen, progesterone, and oocytes

Prolactin

Released from anterior pituitary when stimulated by prolactin-releasing factor (PRF) from hypothalamus

Non tropic

Lactation, Supply and demand

Positive feedback

Oxytocin

Urine stretching/Nipple suckling stimulates hypothalamus to make oxytocin, released by posterior pituitary

Causes increased uterus contractions/release of milk

Positive feedback

Non tropic

Supply and demand

Anti diuretic hormone (ADH)

Reduces urine production to keep water in body, increasng blood volume and pressure

Pancreas Endocrine Function

pancreatic islets (endocrine cell clusters) maintain homeostasis by regulating blood sugar levels

Pancreas detects rising blood glucose levels after eating, alpha cells secrete insulin which goes to body cells and liver

Pancreas detects declining blood glucose levels when fasting, beta cells secrete glucagon which stimulates liver to release stored glucose