BISC 221 - Endocrinology (Topic 7) - Midterm 3

The Body’s Long-Distance Regulators

Animal hormones are chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body

Where do hormones travel and which cells respond?

Hormones reach all parts of the body, but only target cells have receptors for that hormone

What is the function of the endocrine system?

Chemical signaling by hormones

What is the nervous system?

A network of specialized cells—neurons—that transmit signals along dedicated pathways

How do the nervous and endocrine systems interact?

The nervous and endocrine systems often overlap in function

What are the two criteria used to classify intercellular communication?

The type of secreting cell and the route taken by the signal in reaching its target

What is endocrine signaling?

Hormones secreted into extracellular fluids by endocrine cells reach their targets via the bloodstream

What does endocrine signaling maintain and regulate?

Endocrine signaling maintains homeostasis, mediates responses to stimuli, regulates growth and development

What are local regulators?

Molecules that act over short distances, reaching target cells solely by diffusion

What is paracrine signaling?

The target cells lie near the secreting cells e.g. growth factors

What is autocrine signaling?

The target cell is also the secreting cell e.g. cytokines

What is synaptic signaling?

Neurons form specialized junctions with target cells, called synapses

What do neurons secrete at synapses?

Molecules called neurotransmitters that diffuse short distances and bind to receptors on target cells

What is neuroendocrine signaling?

Specialized neurosecretory cells secrete molecules called neurohormones that travel to target cells via the bloodstream

What are the three major classes of hormones?

Polypeptides, steroids, and amines

Which hormones are water-soluble?

Polypeptides and amines

Which hormones are lipid-soluble?

Steroid hormones and other largely nonpolar hormones

How are water-soluble hormones secreted and transported?

Secreted by exocytosis, travel freely in the bloodstream, and bind to cell-surface receptors

How do lipid-soluble hormones travel and bind?

Diffuse across cell membranes, travel in the bloodstream bound to transport proteins, and diffuse through the membrane of target cells

Where do lipid-soluble hormones bind?

Receptors in the cytoplasm or nucleus of the target cells

What happens when a hormone binds to its receptor?

Initiates a signal transduction pathway

What can signal transduction lead to?

Changes in the cytoskeleton, enzyme activation or gene expression

What hormone mediates short-term stress response?

Epinephrine

What does epinephrine bind to in liver cells?

Receptors on the plasma membrane of liver cells

What does epinephrine trigger?

The release of messenger molecules that activate enzymes and result in the release of glucose into the bloodstream

What is the typical response to lipid-soluble hormones?

A change in gene expression

What happens when a steroid hormone binds to its cytosolic receptor?

A hormone-receptor complex forms that moves into the nucleus

What does the receptor do in the nucleus?

Acts as a transcriptional regulator of specific target genes

What are steroid hormones chemically derived from?

Cholesterol

How do steroid hormones enter target cells?

Passing through the cell membrane

Where do steroid hormones bind?

Intracellular receptor

What do steroid hormones activate?

Specific genes to produce specific proteins

How fast do steroid hormones act?

Slower acting than nonsteroid hormones; minutes to hours

Why do steroid hormones act slowly?

Because they need to activate DNA and form new proteins

Why do their actions last a long time?

Because they activate DNA and form new proteins

What are nonsteroid hormones?

Water soluble

Where do nonsteroid hormones bind?

Receptors on target cell membranes

How do nonsteroid hormones work?

Through intermediate mechanisms to activate existing enzymes

What second messenger may be involved?

Cyclic AMP (cAMP)

How fast do nonsteroid hormones act?

Faster action than steroid hormones; seconds to minutes

Why do nonsteroid hormones act quickly?

Because they only need to change existing proteins

Why are their actions short-lived?

Because they only change existing proteins

How do nonsteroid hormones act?

Indirectly through signaling pathways

Why can the same hormone have different effects?

Different receptors for the hormone or different signal transduction pathways

What is an example of epinephrine effects?

Increase blood flow to major skeletal muscles, but decrease blood flow to the digestive tract

What are endocrine glands?

Ductless organs called endocrine glands

Examples of endocrine glands?

Thyroid and parathyroid glands, testes, and ovaries

What are exocrine glands?

Have ducts to carry secreted substances onto body surfaces or into body cavities

What is common in endocrine signaling?

Feedback regulation and coordination with the nervous system

How do hormones act in regulatory pathways?

Released from an endocrine cell, travel through the bloodstream, and interact with specific receptors within a target cell to cause a physiological response

What example involves secretin?

Acidic contents of the stomach into the duodenum stimulates endocrine cells there to secrete secretin

What does secretin cause?

Target cells in the pancreas to raise the pH in the duodenum

What is a simple endocrine pathway?

Hormone released → travels through bloodstream → interacts with target cells → response

What is negative feedback example?

Low pH in duodenum → bicarbonate release

What is a simple neuroendocrine pathway?

Stimulus received by sensory neuron, stimulates neurosecretory cell

What does the neurosecretory cell do?

Secretes a neurohormone into bloodstream

What example involves oxytocin?

Suckling stimulates hypothalamus → release of oxytocin → mammary glands secrete milk

What is negative feedback?

Inhibits a response by reducing the initial stimulus, thus preventing excessive pathway activity

What is positive feedback?

Reinforces a stimulus to produce an even greater response

What does the hypothalamus do?

Receives information from the nervous system and initiates responses through the endocrine system

What is attached to the hypothalamus?

Pituitary gland

What are the parts of the pituitary gland?

Posterior pituitary and anterior pituitary

What does the posterior pituitary do?

Stores and secretes hormones that are made in the hypothalamus

What does the anterior pituitary do?

Makes and releases hormones under regulation of the hypothalamus

What hormones are synthesized by the hypothalamus for the posterior pituitary?

Antidiuretic hormone (ADH) and Oxytocin

What does ADH regulate?

Water reabsorption

What does oxytocin regulate?

Milk secretion by the mammary glands

How is anterior pituitary hormone production controlled?

By releasing hormones and inhibiting hormones from the hypothalamus

What does prolactin do?

Role in milk production

What does TSH do?

Stimulates growth of the thyroid gland and secretion of thyroid hormone

What does ACTH do?

Stimulates growth of the adrenal cortex and secretion of cortisol—increases blood glucose in response to stress

What does prolactin do in women?

Stimulates growth of the mammary glands and production of milk

What does GH do?

Causes generalized body growth

What are LH and FSH?

Gonadotropins

What do gonadotropins control?

Secretion of sex hormones by the gonads

What happens when thyroid hormone levels drop?

Hypothalamus secretes TRH

What does TRH do?

Causes anterior pituitary to secrete TSH

What does TSH do?

Stimulates thyroid gland to secrete T3 and T4

What is the feedback mechanism?

Thyroid hormone blocks TRH and TSH release

What does thyroid hormone regulate?

Many functions in humans and other mammals

What does the thyroid gland secrete?

T3 and T4

What do T3 and T4 affect?

Basal metabolic rate (BMR)

What are T3 and T4 important for?

Cellular conversion of glucose to ATP

What is hypothyroidism?

Thyroid secretes too little T3 and T4

Effects in children?

Mental retardation and stunted bone growth

Effects in adults?

Slow heart rate, low body temperature, muscular weakness, general tiredness, tendency to gain weight

What is hyperthyroidism?

Oversecretion of thyroid hormones

What is Graves disease?

BMR can be 60 to 100 percent above normal, fluid builds up behind the eyes

What is goiter?

Overproduction of TSH results in an enlarged thyroid

How can goiter be prevented?

Adding iodine to the diet

What does growth hormone (GH) do?

Promotes growth directly and stimulates production of growth factors

What happens with excess GH?

Gigantism

What happens with lack of GH?

Dwarfism

What is acromegaly?

Excess GH after bones stop growing

What does PTH do?

Increases blood Ca2+

How does PTH increase Ca2+?

Releases Ca2+ from bone and stimulates reabsorption in kidneys

What does calcitonin do?

Decreases blood Ca2+

How does calcitonin act?

Stimulates Ca2+ deposition in bones and inhibits uptake by kidney

What is glucose used for?

Major fuel for cellular respiration and carbon skeletons for biosynthesis

What hormones regulate glucose?

Insulin and glucagon