Body Regulation

Endocrine Systems

Principles of Endocrine Control

- endocrine glands: ductless glands secreting chemical messengers (hormones) which diffuse directly into blood and carried to target organs to exert a specific physiological effects

Nervous co-ordination gives rapid control.Endocrine co-ordination regulates long-term

changes.

The two systems interact in a dynamic way in order to maintain the constancy of the animal's internal environment, while permitting changes in response to a varying external environment.

Both systems secrete chemicals, the nervous system as a transmitter between neurones and the endocrine system as its sole means of communication between various organs and tissues in the body. .

Chemistry of Hormones Steroids - oestrogen, progesterone, testosterone,

cortisone, aldosterone Polypeptides (less than 100 amino acids) -

oxytocin, insulin, glucagon, antidiuretic hormone (vasopressin)

Amines - adrenaline, noradrenaline, thyroxine Proteins - prolactin, follicle stimulating

hormone, luteinizing hormone, thyroid stimulating hormone, adrenocorticotrophic hormone, growth hormone

Pituitary gland- The “master” endocrine gland. Controls other endocrine glands

The Hypothalamus & the Pituitary The Hypothalamus & the Pituitary Gland-- Master Endocrine Glands!Gland-- Master Endocrine Glands!

The Hypothalamus: Located in the brain,

this region controls most endocrine secretions

Mainly regulatory hormones are released here. Most control the pituitary gland

The Pituitary Gland Descending from the

hypothalamus, this gland has two halves: anterior & posterior

The anterior half secretes mainly regulatory hormones

The posterior half secretes hormones, but manufactures none

The Posterior Pituitary LobeThe Posterior Pituitary Lobe

No hormones are made here. They are made in the hypothalamus and just released here.

Two peptide hormones are released from the posterior pituitary lobe (the neurohypophysis):

ADH (antidiuretic hormone or vasopressin) OT (oxytocin)

Function of Posterior Pituitary Lobe Function of Posterior Pituitary Lobe HormonesHormones

ADHosmoregulation as an “antidiuretic,” ADH

decreases urine formation by having kidneys conserve water

also can contract smooth muscle cells, as found in blood vessels-- this causes an increase in blood pressure

ADH release triggered by osmoreceptors and inhibited by stretch receptors in blood vessels

OT: In females, contracts

the uterine wall smooth muscles

In females, helps to eject milk when lactating

No known function in males, although in both males and females, OT can have some antidiuretic effects

LactationLactation

In females, PRL promotes milk synthesis Milk release is stimulated by oxytocin Milk contains an inhibitory peptide to stop

lactation when not required. In males, PRL decreases LH secretion (note

that too much PRL would then decrease androgen levels and cause sterility)

Hormones secreted by the Hypothalamus & Hormones secreted by the Hypothalamus & Anterior Pituitary GlandAnterior Pituitary Gland

Hypothalamus Anterior PituitaryGHRH (GH-releasing) GH (growth hormone)

SS (somatostatin, GH-inhib) “CRH (corticotropin-rel) ACTH

(adrenocorticotropic)

GnRH (gonadotropin-rel) LH (luteinizing hormone)

“ FSH (follicle-stimulating)

PRH (PRL-releasing) PRL (prolactin)

PIH (PRL rel-inhibiting) “TRH (thyrotropin-rel) TSH (thyroid stimulating)

What do these anterior pituitary What do these anterior pituitary hormones do?hormones do?

Growth Hormone: stimulates cells to grow

and divide increases amino acid

transport rate and protein synthesis

increases fat metabolismTypically, GH is secreted

during sleep.GH secretion increases

when malnourished

GH influences bone growth via somatomedin:

GH in bloodGH arrives in liverliver secretes

somatomedincartilage dividesbones grow!

Hormones of the complex– releasing hormones

of the hypothalamus• TSHr

– ant. pituitary hormones: thyrotropin

– thyroxine

How are hormones regulated?How are hormones regulated?Hypothalamus-Pituitary-ThyroidHypothalamus-Pituitary-Thyroid

Thyroid

Negative Feedback

Click for animation

thyroid– thyroxine (T4),

triiodothyronine (T3)• increase oxidative metabolism• protein distribution and

metabolism

Hormones of the thyroidHormones of the thyroid

About the Thyroid Hormones...About the Thyroid Hormones...

T3 and T4: Function: metabolism regulation (break

down carbohydrates and fats, synthesize proteins)

Can only be made by follicular cells when iodides are available

Somewhat hydrophobic and get carried by proteins in the blood.

T3 more effective, T4 more abundant

Problems with the Thyroid GlandProblems with the Thyroid Gland

Hyperthyroidism: high metabolic rate, hyperactivity, sensitivity to heat, protruding

eyes Grave’s disease: when hyperthyroidism is due to an

autoimmune problem (TSH is mimicked by autoantibodies)

Hypothyroidism: in the adult: low metabolic rate, sensitivity to cold,

sluggishness in an infant: cretinism-- stunted growth, mental retardation,

abnormal bone formation goiter: no T3 and T4 can be made because not enough

iodides were ingested.

Goiter- without iodine, functional hormones cannot be made. Lack of iodine in our diet can lead to enlargement of thyroid gland (goiter) Uncommon in U.S. because of iodized salt

Pancreas- Produces insulin and glucagon

1. Regulates the metabolism of glucose (sugar)

2. Insulin decreases sugar and glucagon increases glucose levels.

3. Diabetes mellitus- condition where there is an undersecretion of insulin. Results in high level of glucose in blood.

Adrenal Glands- pyramid-shaped structures that sit on kidneys

1. Produces adrenaline (also called epinephrine) released during “fight or flight” situations

2. Increases blood glucose level, heart rate.

Hormones of the Adrenal GlandsHormones of the Adrenal Glands

Adrenal Medulla produces two hormones that regulate the “fight or flight” response– adrenalin (epinephrine)– noradrenalin (norepinephrine)

Hormones of the Adrenal GlandsHormones of the Adrenal Glands

Adrenal Cortex produces many hormones– steroids

• glucocorticoids (cortisol, corticosterone, cortisone)– cause a rise in blood sugar

Hormones of the Adrenal GlandsHormones of the Adrenal Glands

Adrenal Cortex produces many hormones– steroids

• mineralcorticoids (e.g., aldosterone)– regulates bp, bv, salt balance,

Other Endocrine GlandsOther Endocrine Glands

Reproductive glands (the gonads): the ovaries and the testes produce sex hormones

Reproductive Glands (the gonads)

1. Male gonads (testes) produce sperm. Control growth of facial hair, increase body size, deepening of voice, etc. (testosterone)

Female gonads (ovaries) produce eggs (ova). Control widening of hips, development of breasts, prepares uterus for arrival of developing embryo (estrogens, progesterone)

Negative Feedback of HormonesNegative Feedback of Hormones

Low concentrations of a particular hormone result in increased secretion of that hormone, and when the concentration reaches a certain level, secretion is reduced

Control of the Endocrine System

A. Regulated by negative-feedback mechanism that functions to maintain homeostasis

1. When target tissue responds to hormone- sends chemical back to gland

2. Gland stops producing hormone

3. If level of hormone to low- gland signaled to start secretion of hormone again

B. Automatic and self-regulating

Blood Glucose Regulation by the PancreasBlood Glucose Regulation by the PancreasGlucagon:It works on the liver to

cause the production of glucose via:– glycogenolysis– gluconeogenesis

It is regulated by blood glucose levels directly:– secreted when blood

glucose drops (before next meal)

Prevents hypoglycemia

Insulin:

It works on the liver to remove glucose from the blood via:– making glycogen– preventing gluconeogenesis– increasing glucose transport

into cells

It is also regulated by blood glucose levels directly

Prevents hyperglycemia

Note: glucagon and insulin work in opposition, and their combined effects control blood glucose

Pancreas: Regulation of GlucosePancreas: Regulation of Glucose

Diabetes results from pancreatic malfunction or receptor malfunction– alpha cells secrete glucagon (release of glucose)– beta cells secrete insulin (uptake of glucose)

Balance of glucagon and insulin determine blood glucose levels