The Endocrine System

ADRENAL GLANDS

Primary function of the adrenal glands is to control electrolyte levels in the body

Adrenal Cortex

has 3 layers

each layer secretes a particular hormone called a steroid

AHN P.502

Electrolytes: mineral substances such as potassium

PANCREAS

Other functions of the adrenal glands:

assists in regulating metabolism

Objective #1

Pancreatic islets: parts of the pancreas that have endocrine functions

interacts with the SNS in response to stress

Define key terms:

Secretions of the Adrenal Medulla

Secretions of the Adrenal Cortex

Functions:

(fight or flight)

Epinephrine: a.k.a. andrenaline

Androgens:

sex hormones secreted by the gonads, the adrenal cortex, and fat cells

stimulates the sympathetic nervous system (SNS) in response to injury or stress

Corticosteroids:

steroid hormones produced by the adrenal cortex

Norepinephrine:

aldosterone: regulates the salt and water levels by increasing Na+ reabsorption & potassium excretion by kidneys

Reabsorption:

returning a substance to the bloodstream

both a hormone (adrenal medulla) and a neurohormone (SNS)

control of blood sugar levels and glucose metabolism

Let's get start with an overall review!

cortisol: a.k.a. hydrocortisone

has an inflammatory action

plays a role "fight or flight": increase HR & BP, stimulates muscle contraction

Key Terms:

Catecholamines: hormones that naturally occur in the body: dopamine, norepinephrine, and epinephrine.

The body produces more catecholamines during times of stress.

They make your heart beat faster, your blood pressure rise, and in general prepare your body to respond to stress.

Neurohormones: produced and released by neurons in the brain as opposed to endocrine glands

regulates the metabolism of CHO, fats, & PRO

delivered to organs and tissues through the bloodstream

Norepinephrine: is similar to adrenaline. It works by constricting (narrowing) the blood vessels and increasing blood pressure and blood glucose (sugar) levels.

a.k.a. noradrenaline

Pancreatic islet secretions:

glucose:

basic form of energy for the body

glucagon:

Pancreas: has endocrine and excroine function

hormone secreted by alpha cells in response to low glucose levels

Influences CHO metabolism

increases glucose levels by stimulating the liver to convert glycogen into glucose

Indirectly influences fat & PRO metabolism

insulin:

Produces insulin and glucagon

hormone secreted by the beta cells in response to high glucose levels

Insulin

When energy is needed, insulin allows glucose to enter the cells to be used for this energy

PARATHYROID GLANDS

When additional glucose is not needed, insulin stimulates the liver to convert glucose into glycogen for storage

About the size of a grain of rice

Embedded in the posterior surface of the thyroid gland

Regulates calcium levels throughout the body via secretion of Parathyroid Hormone (PTH)

Parathyroid Hormone

Parathyroid Hormone (PTH)

Works with calcitonin

Parathyroid Hormone

Influences the kidney in two ways:

PTH- secreted to increase blood levels of calcium by stimulating its release from bones & teeth

• PTH controls calcium and phosphorus levels in the blood.

increases the reabsorption of Ca++ & Mg++

13 Endocrine Glands- PITUITARY GLAND

also regulates serum phosphorus

If the blood calcium level is too low, the parathyroid glands release more PTH:

accelerates the elimination of phosphorus in the urine

• This causes the bones to release more calcium into the blood and reduces the amount of calcium released by the kidneys into the urine

• Vitamin D is converted to a more active form, causing the intestines to absorb more calcium and phosphorus.

Through negative feedback controls the activity of other endocrine glands via hormone secretion

If the calcium level is too high, the parathyroid glands release less PTH, and the whole process is reversed.

Low Ca++

tetany

Works closely with the hypothalamus

PTH levels that are too high or too low can cause problems with the kidneys and bones and cause changes in calcium and vitamin D levels.

THE THYROID GLAND

Hypothalamus

is part of the nervous system that produces hormones that control many body functions

Activates, controls, and integrates the peripheral autonomic nervous system, endocrine processes, & many somatic functions i.e. body temperature, sleep, appetite

Pituitary Gland

Pituitary Segments

Each segment produces specialized hormones

Called the "master gland"

The hypothalamus produces the hormones of the posterior pituitary

Hypothalamus then releases them to be stored in the posterior pituitary gland

Hormones are released from the posterior pituitary gland as a result of nerve impulses received by the hypothalamus

Promotes growth of body tissue

Influences water absorption by the kidneys

Controls the the rate of body metabolism (primary function) and growth

Secretes 6 Major Hormones

Somatotropin or growth hormone (GH)

Two hormones are released when this gland is stimulated by the hypothalamus:

Adrenocorticotropic hormone (ACTH)

Thyroid-Stimulating Hormone (TSH)

Oxytocin

Antidiuretic hormone

Controls sexual development and function

Anterior Pituitary Gland

Posterior Pituitary Gland

(adenohypophysis)

(neurohypophysis)

Prolactin

Posterior pituitary gland stores both these hormones that are synthesized by the hypothalamus

Gonadotrophic Hormones:

Follicle-stimulating hormone (FSH)

Lutenizing Hormone (LH)

Anterior Pituitary Gland Hormones

Tropic Hormones: responsible for the stimulation of other endocrine glands

Somatotropin hormone

Adrenocorticotropic hormone

Thyroid-stimulating hormone

Follicle-stimulating hormone

Luteinizing hormone

Prolactin: nontropic hormone

Metabolism: all the processes involved in the body's use of nutrients, including the rate at which they are used

Pituitary Gland Anterior Lobe Hormones

Melanocyte-stimulating Hormone (MSH)

Interstitial cell-stimulating Hormone

Adrenocorticotropic Hormone (ACTH)

Thyroid-stimulating Hormone (TSH)

Growth Hormone (GH)

Follicle-stimulating Hormone (FSH)

Luteinizing Hormone (LH)

Prolactin Stimulating Hormone

(a.k.a. melanotropin)

(a.k.a. somatotropic hormone)

(a.k.a. lactogenic hormone (LTH))

Stimulates ovulation in the female

Stimulates the secretion of estrogen and the growth of ova (eggs) in the ovaries of a woman

Stimulates ovulation in the female

Stimulates the secretion of hormones by the thyroid gland

Increases the production of melanin in melanocytes- causes darkening of skin

Stimulates the growth and secretions of the adrenal cortex

Nontropic hormone

Regulates the growth of bone, muscle, and other body tissues

Stimulates secretion of testosterone in the male

Stimulates secretion of testosterone on males

stimulates and maintains the secretion of breast milk in the mammary glands

Stimulates the production of sperm in the testicles (testes) of males

MSH production usually increases during pregnancy

Controls the production of thyroxine (T4), triiodothyronine (T3), & calcitionin (thyrocalcitonin)

Thyroid Stimulating Hormone (TSH)

T3 & T4

Regulate 3 main functions:

growth & development

THYMUS GLAND

metabolism

Produced by the anterior lobe of the pituitary gland

activity of the nervous system

Regulates the secretion of both:

T4 & T3

Adequate intake of iodine is necessary for thyroid hormone formation

Thyrotropin

• Secreted by the hypothalamus

• Triggers the pituitary gland to release TSH.

Secretes a hormone that affects the immune system

• Can also stimulates the release of Prolactin from the pituitary gland

Calcitonin

Hormone that works with the parathyroid hormone to regulate calcium levels in the blood and tissues

Influence the growth and the function of the nervous system

Calcitonin works to decrease calcium levels in the blood and tissues

Facilitates the movement of calcium into bones and teeth for storage

Hormone: thymosin

Thymosin: stimulates the maturation of lymphocytes into T cells

Define Key Terms

Gland:

specialized group of cells and tissues that work together to produce and secrete substances such as:

enzymes

hormones

Hormones:

chemical messengers that travel through the blood stream to their target organs

metabolic changes occur in response to the actions of hormones

hormones can increase or decrease a normal body process by affecting a target organ

hormones secreted by the endocrine system work closely with the nervous system

amount of hormone released is controlled by negative feedback inhibition

Endocrine glands secrete their hormones directly into the bloodstream

Divided into two categories:

Exocrine:

A gland that secretes a substance out through a duct

-discharge it into the external environment, to organs or the outside the body

-Examples of exocrine glands are sweat, saliva and mammary glands

Endocrine Glands

Exocrine

Endocrine

Many endocrine glands are linked to neural control centers by homeostatic feedback mechanisms

The two types of feedback mechanisms are negative feedback and positive feedback

In positive feedback mechanisms, the original stimulus is promoted rather than negated. Positive feedback increases the deviation from an ideal normal value. Unlike negative feedback that maintains hormone levels within narrow ranges, positive feedback is rarely used to maintain homeostatic functions.

Negative feedback decreases the deviation from an ideal normal value, and is important in maintaining homeostasis

Most endocrine glands are under the control of negative feedback mechanisms

An example of positive feedback can be found in childbirth. The hormone oxytocin stimulates and enhances labor contractions. As the baby moves toward the vagina (birth canal), pressure receptors within the cervix (muscular outlet of uterus) send messages to the brain to produce oxytocin. Oxytocin travels to the uterus through the bloodstream, stimulating the muscles in the uterine wall to contract stronger (increase of ideal normal value). The contractions intensify and increase until the baby is outside the birth canal. When the stimulus to the pressure receptors ends, oxytocin production stops and labor contractions cease.

Negative Feedback Inhibition

a target gland releases a hormone

stimulates target cells to release another hormone

the gland slows the release of its hormone as it senses the amount of the second hormone increasing

Endocrine Glands

~ Ductless glands that release their secretions (hormones) directly into the blood stream

~ Secretions have a regulatory function

~ have a generalized effect on the metabolism, growth, development, reproduction, & other bodily activities such as:

temperature

fluid balance

Negative feedback mechanisms act like a thermostat in the home. As the temperature rises (deviation from the ideal normal value), the thermostat detects the change and triggers the air-conditioning to turn on and cool the house. Once the temperature reaches its thermostat setting (ideal normal value), the air conditioning turns off.

emotional responses

THERE ARE 13 MAJOR GLANDS THAT MAKE UP THE ENDOCRINE SYSTEM

13 MAJOR ENDOCRINE GLANDS

Endocrine Functions

One pituitary gland

One pineal gland

One thyroid gland

Reproduction

Energy metabolism

Response to stress or injury

Maintenance and regulation of vital functions

Growth and development

Acid-base balance, fluids & electrolytes

Four parathyroid glands

One thymus

One pancreas (pancreatic islets)

Two adrenal glands

Two gonads (either a pair of ovaries in females or a pair if testicles in males)

THE GONADS

Gonads: gamete-producing glands

Gamete: reproductive cell- sperm & ova

secrete hormones that are responsible for the development & maintenance of secondary sex characteristics during puberty

Secondary sex characteristics: refers to fetures that distinguish btwn. male and female, not directly r/t reproduction

PINEAL GLAND

Hormones secreted by the Gonads

Estrogen:

secreted by the ovaries

Located in the central portion of the brain

Hormones secreted by the Gonads

important for the development and maintenance of female secondary sex characteristics

Progesterone:

released during the second half of the menstrual cycle by the ovary

functions to complete the preparation of the uterus for pregnancy

Androgens:

sex hormones, primarily testosterone

also secreted by the adrenal cortex and fat cells

involved with regulation of the menstrual cycle

promotes the development and maintenance of male sex characteristics

Hormone melatonin influences the sleep- wakefulness cycle

present in both men and women

Gonadotropin:

any hormone that stimulates the gonads

Testosterone:

secreted by the testicles and the adrenal cortex

stimulates male secondary sex characteristics

The Endocrine System

Hormone Production & Homeostasis