Hormones and the Endocrine system

chapter 45

By: Allysa Yi,

Gunjan Nachane,

Michael Wormley,

and Vickie Eickelberg

Hormones: a molecule that’s secreted into the extracellular fluid, circulates in blood or hemolymph, and communicates regulatory messages throughout the body.

Local Regulators: secreted molecules that act over short distances and reach their target cells by diffusion.

Hormones & Local Regulators (#1)

Basic path of a hormone. Hormones travel through the bloodstream. In contrast, a local regulator would diffuse from its origin to its target cell through diffusion.

Paracrine signaling: target cells lie near the secreting cell. Autocrine signaling: secreted molecules act on the secreting cell

itself. Neurohormone: A specific class of hormones secreted by

neurosecretory cells that secrete the neurohormones and once secreted they travel from nerve cell endings into the bloodstream.

Ex: Vasopressin which is critical to kidney function and water balance.

Secreted to the bloodstream and a target cell

Diffused locally to trigger response in neighbor cells

Diffused locally to trigger response in cells that secrete them

Diffused into the bloodstream to trigger a response in a target cell

Paracrine vs Autocrine (#2&3)

Polypeptides (proteins and peptides): water soluble, made of polypeptide chains or from cleavage of longer protein chains. Ex: Insulin

Amines: water soluble, made from single amino acid. Ex: Epinephrine

Steroids: Lipid soluble and pass through cell membranes readily, made from four fused carbon rings. Ex: Cortisol

3 Major Classes of Molecules (#4)

Major Classes of hormones summarized into peptides, steroids, and amino acid derivative (Amines)

Intracellular Receptors in Steroid Hormones (#5)

The hormone estradiol, a form of estrogen was studied. Experimented on rats by treating them with radioactive forms of estradiol. Results: Hormone accumulated in the nuclei. Showed that the receptors for steroid hormones are indeed inside the

cell.

The path of a steroid hormone. Important to notice how it diffuses through the plasma membrane.

• Binding of a hormone to its receptor initiates a signal transduction pathway, a series of changes in cellular proteins that converts an extracellular chemical signal to a specific intracellular response.•Receptors for most water–soluble hormones are embedded in the plasma membrane. They are secreted by exocytosis, travel freely in bloodstream, and bind to cell-surface receptors•Depending on the hormone and target cell, the response may be:

•Activation of an enzyme•A change in the uptake or secretion of specific molecules•Rearrangement of the cytoskeleton. •Signal transduction from some cell–surface receptors activates proteins in the cytoplasm that then move into the nucleus and directly or indirectly regulate transcription of specific genes.

OR

Water-Soluble Hormones (#6)

Pathway of water-soluble hormones.

Intracellular receptors are found either in the cytoplasm or in the nucleus of the target cell.

Lipid-soluble hormones (steroid hormones) pass easily through cell membranes, while water-soluble hormones (polypeptides and amines) do not.

Lipid-soluble hormones diffuse across cell membranes, travel in the bloodstream bound to transport proteins, and diffuse through the membrane of target cells.

Lipid-soluble hormones are different than signal-transduction pathway/water-soluble because lipid-soluble hormones activate the receptor which directly triggers the cell’s response.

Lipid-Soluble Hormones (#8)

Target cells with the same receptor exhibit different responses if they have different signal transduction pathways and/or effector proteins. Responses of target cells may also differ if they have different receptors for the hormone.

The effects brought about by a particular hormone can vary if target cells differ in the molecules that receive or produce the response to that hormone.

Diverse Response (#7)

Paracrine Signaling: Local regulators convey messages

between neighboring cells.

Cytokines: plays a role in immune responses.

Growth factors: stimulate cell proliferation and differentiation.

Nitric oxide (NO): Serves in the body as both a neurotransmitter and a local regulator. NO activates an enzyme that relaxes neighboring smooth muscle cells, dilating the walls of blood

vessels and improving blood flow to tissues. Highly reactive NO usually triggers changes in the target cell within a few seconds of contact and then

breaks down. When secreted by white blood cells, it kills bacteria and cancer cells.

Prostaglandins (PG): In the immune system, prostaglandins promote fever and inflammation and intensify the sensation of

pain which contribute to the body’s defense. They help regulate aggregation of platelets, an early step in formation of blood clots. They regulate nearby cells in various ways, depending on the tissue. In semen that reaches the female reproductive tract, prostaglandins trigger the contraction of the

smooth muscles of the uterine wall, helping sperm to reach the egg. PGs secreted by the placenta cause the uterine muscles to become more excitable, helping to induce

uterine contractions during childbirth. Prostaglandin E signals the muscle cells to relax, dilating the blood vessels and promoting oxygenation

of the blood. Prostaglandin F signals the muscle cells to contract, constricting the vessels and reducing blood flow

through the lungs.

Local Regulators in Paracrine Signaling (#9)

Negative feedback: a loop in which the response reduces the initial stimulus.

An example is insulin. Insulin is released when there are high levels of glucose and insulin decreases it by taking it in and reaches homeostasis.

Simple hormone pathway: Hormones are released from an endocrine cell, travel through the bloodstream, and interact with specific receptors within a target cell to cause a physiological response.

Example is secretin signaling in the endocrine system. (Picture to the right).

Stimulus

Endocrinecell

Hormone

Bloodvessel

Targetcells

Response

S cells of duodenumsecrete the hormonesecretin ( ).

Low pH in duodenum

Pancreas

Bicarbonate release

ExamplePathway

Simple Hormone Pathway with Negative Feedback #10

Example of a Simple Pathway

Steroid Hormones are also called _____________ and their receptors are located inside or outside the cell?

Where can you find most of the receptors for water-soluble hormones? Why?

Comprehension Checks

Answer is… Steroid Hormones are also called lipid-soluble

hormones and their receptors are located inside or outside the cell?

Where can you find most of the receptors for water-soluble hormones? Why?Embedded in the plasma membrane and because

they cannot pass easily through cells.

Comprehension Checks1. Growth factors are local regulators that

A. Are modified fatty acids that stimulate bone and cartilage growth

B. Are found on the surface of cancer cells and stimulate abnormal cell division

C. Are proteins that bind to cell-surface receptors and stimulate growth and development of target cells

D. Convey messages between nerve cells

Answer is…

C

Body cells take up more glucose

Insulin

Liver takes up glucose and stores it as glycogen.

Beta cells of pancreas release insulin into the blood.

Stimulus: blood glucose level rises

Homeostatis:Blood glucose level

Stimulus: blood glucose level falls

Alpha cells of pancreas release glucagon into the blood.

Glucagon

Liver breaks down glycogen and releases glucose into the blood

Blood glucose level rises

Blood glucose level decreases

Insulin vs. Glucagon (#11)

Antagonistic Hormones• 2 hormones that regulate

a function• Their effects are opposite

on the body

Insulin: Secreted by the beta cells of the pancreas and decreases blood glucose level.

Glucagon: Secreted by the alpha cells of the pancreas and increases blood glucose level.

Type 1 Diabetes:-Immune system destroys beta cells of pancreas, which leads to insulin deficiency.

-Appears during childhood

Type 2 Diabetes:-Failure of target cells to respond normally to insulin

-Individual still makes insulin, but blood glucose levels are high

-Correlated with obesity

Type 1 and 2 Diabetes ( #12)

Hormone Secreted by Action

Growth hormone Anterior pituitary gland Stimulates bone growth

FSH, LH Anterior pituitary gland Stimulates ovaries and testes

TRH Hypothalamus Indirectly causes release of TSH

Prolactin Anterior pituitary gland Stimulates milk production and secretion

Calcitonin Thyroid Lowers blood calcium level

PTH Parathyroid Raises blood calcium level

Glucagon Pancreas Raises blood glucose level

Insulin Pancreas Lowers blood glucose level

Testosterone Testes Supports sperm formation and secondary sex characteristics

Estradiol Ovaries Stimulates uterine lining growth and secondary sex characteristics.

Invertebrate

Hormones (#13)

Hypothalamus

Posteriorpituitary Anterior

pituitary

Hormone Prolactin GH FSH TSH LH ACTH

Function Milkproduction

GrowthOva andsperm

Increasesiodine

Ovaries/testes Stimulates adrenal cortex

Hormones produced by posterior pituitary

-ADHGoes to kidney tubules

-OxytocinGoes to mammary glands, uterine muscles

Hypothalamus and Pituitary Glands(#14 & 15)

Comprehension Check

Type 1 diabetes mellitus is caused by a deficiency of ________

A. exercise

B. glucagon

C. glucose

D. glycogen

E. insulin

Answer is…

E

Suckling stimulates sensory nerve cells in the nipples, which send nervous signals that reach the hypothalamus, the control center.

The hypothalamus triggers the release of the neurohormone oxytocin from the posterior pituitary gland.

Oxytocin causes the mammary glands to secrete milk. The release of milk in turn leads to more suckling and stimulation of the pathway, until the baby is full.

Positive Feedback by Oxytocin Signaling (#16)

All four anterior pituitary tropic hormones participate in complex neuroendocrine pathways.

In each pathway, signals to the brain stimulate release of an anterior pituitary tropic hormone.

The tropic hormone then acts on its target endocrine tissue, stimulating secretion of a hormone that exerts systemic metabolic or developmental effects.

http://www.bing.com/videos/search?q=tropic+hormones&view=detail&mid=949D146F3747DAD29500949D146F3747DAD29500&first=0&FORM=NVPFVR

Tropic Hormones (#17)

The thyroid gland produces two very similar hormones derived from the amino acid tyrosine: triiodothyronine (T3), which contains three iodine atoms, and thyroxin (T4), which contains four iodine atoms.

Throughout the body, T3 and T4 are important in bioenergetics, increasing the rate of oxygen consumption and cellular metabolism.

In addition to cells that produce T3 and T4, the mammalian thyroid gland produces calcitonin. Rigorous homeostatic control of blood calcium

level is critical to cell function.

When blood Ca2+ falls below the set point,

parathyroid hormone (PTH) is released

from four small structures,

the parathyroid glands,

embedded on the surface of the thyroid.

Thyroid Gland and Parathyroid Glands (#18 & 19)

In mammals, each adrenal gland is actually made up of two glands with different cell types, functions, and embryonic origins. The adrenal cortex is the outer portion, and the adrenal medulla is the central portion.

The adrenal medulla produces two hormones, epinephrine (adrenaline) and norepinephrine (noradrenaline).

Either positive or negative stress stimulates secretion of epinephrine and norepinephrine from the adrenal medulla.

Hormones of Adrenal Medulla (#20)

Comp Check (Check yo Comp)Question 1:

The hypothalamus triggers the release of the neurohormone _____________

Question 2:

The thyroid gland produces two very similar hormones ____ and T4.

Question 3:

In mammals, each adrenal gland is actually made up of ___ glands.

Hormones of the Adrenal Cortex (#21) Glucocorticoids: Steroid and raises blood

glucose level. Mineralocorticoids: Steroid and promotes re-

absorption of sodium and excretion of potassium in the Kidneys.

Where the adrenal cortex is located in the adrenal gland. Within the adrenal cortex the hormones are glucocorticoid and mineralcorticoid.

Adrenal gland

The gonads, testes and ovaries, produce most of the sex hormones: androgens, estrogens, and progestins.

The testes primarily synthesize androgens, mainly testosterone, which stimulate development and maintenance of the male reproductive system

Androgens produced early in development determine whether a fetus develops as a male or a female. At puberty, high levels of androgens are

responsible for the development of male secondary sex characteristics, including male patterns of hair growth, a low voice, and increased muscle mass and bone mass typical of males.

Ovaries produce estrogens, most importantly estradiol, which are responsible for maintenance of the female reproductive system and the development of female secondary sex characteristics.

In mammals, progestins, which include progesterone, are primarily involved in promoting uterine lining growth to support the growth and development of an embryo.

Steroid Hormones produced by

gonads(#22)

Male vs. Female

Melatonin Communicates info about light to different parts of the body Regulates a human’s circadian sleep-wake cycle

-Has sleep promoting effects decreases motor activity and increases fatigue

Thought to have a role in reproductive cycles-Allows certain animals to sense a change in season, which indicates that a breeding season has begun

Pineal Gland and Melatonin (#23)

Side of brain