Download The Endocrine System

The Endocrine
System
 Structures
 Functions
The Endocrine System

Homeostasis: the harmonious coordination and integration of all body
functions

Maintaining homeostasis: involves growth, maturation, reproduction and
metabolism

Endocrine system: body system responsible for coordinating homeostasis
through hormone secretion and chemical excretion
The Endocrine System

Composed of numerous glands throughout the body that secrete hormones
into the bloodstream and secrete chemicals to rid the body of wastes.

Chemicals and hormones
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Regulate growth
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Regulate sexual production & development
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Metabolize nutrients in cells
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Maintain homeostasis
Hormones
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Delivered to target cells within the body
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Fit into each cell like a lock and key
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Body sends a signal for a certain hormone when needed (negative
feedback)
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Body responds by producing enzymes
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Enzymes create and release the hormone needed until correction is
complete then secretion stops
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Hormones are made up of four major chemical groups
Hormones - four major
groups
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Fatty acids
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Control hormones involved in estrus
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includes prostaglandins
Steroids
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Occur naturally in the body and regulate chemicals , like
cholesterol, that control essential life functions
Amino acids
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Control thyroid gland functions
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Simplest of the hormones
Peptides
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Control proteins in the body
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Largest of the hormones (example: Oxytocin)
Lock and Key
Hypothalamus
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Located in front of the thalamus
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Serves as a reservoir for hormones
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Closely associated with pituitary gland
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Secretes releasing and inhibiting factors that affect the
release of substances from the pituitary gland
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Produces antidiuretic hormone (ADH) and oxytocin
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Provides a link between the nervous and endocrine
systems
Hypothalamus
Endocrine Glands
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Secrete hormones directly into the bloodstream and then transported to
all areas of the body
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Include the following:

Pituitary

Thyroid

Parathyroid

Adrenal

Thymus
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Pancreas
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Pineal
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Gonads
Pituitary Gland

Main endocrine gland
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Often called the “master gland” because it controls the
thyroid gland.
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Works with hypothalamus to control the endocrine
system and create a link with the nervous system
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Located at the base of the brain

Has an anterior and posterior lobe
Hormones Secreted by the Hypothalamus
HORMONE
FUNCTION
Signals release of Adrenocorticotropic
Corticotropin Releasing
Hormone (ACTH)
Hormone (RH)
Signals release of
Gonadatropin RH
 Follicle Stimulating Hormone
(FSH)
 Luteinizing Hormone (LH)
Growth Hormone RH
Signals release of Growth Hormone (GH)
Growth Inhibiting RH
Thyrotropin RH
Signals inhibition of GH
Prolactin Inhibiting RH
Signals inhibition of Prolactin production
Oxytocin
Antidiuretic Hormone
Synthesized
Signals release of Thyroid-stimulating
hormone (TSH)
Synthesized
Hormones Secreted by the Anterior Pituitary Gland
HORMONE
FUNCTION
ACTH
FSH
LH
Growth Hormone (GH)
TSH
Prolactin (PRL)
Interstitial Cell Stimulating
Hormone (ICSH)
Melanocyte-stimulating
Hormone (MSH)
Glucocorticoid Release
Follicular Development
Ovulation
Corpus Luteum
Androgen Secretion
Promotes growth
CHO
Protein
Lipid
Metabolism
Thyroxine Release
Promotes Lactation
Stimulates ovulation in females
Stimulates androgen release in males
Stimulates melanin synthesis in
melanocytes
Pituitary Gland – Anterior Lobe
Controlled by the hypothalamus
Produces and secretes…
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
• Thyroid-stimulating hormone (TSH): affects growth and
•
•
•
•
•
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secretions of the thyroid gland
Adrenocorticotropic hormone (ACTH): affects growth and
secretions of the adrenal cortex
Follicle-stimulating hormone (FSH): affects the secretion of
estrogen and growth of eggs in the ovaries & production of sperm
in the testes
Lutenizing hormone (LH): affects ovulation and aids in
maintenance of pregnancy in females
Interstitial cell-stimulating hormone (ICSH): stimulates
testosterone secretion in males
Prolactin (lactogenic hormone-LTH): affects milk secretion and
influences maternal behavoir
Growth hormone (somatotropin-STH): accelerates body growth
Melanocyte-stimulating hormone (MSH): affects skin
pigmentation
Pituitary Gland – Posterior Lobe
 Connects
to the hypothalamus
 Does not produce hormones but stores and
secretes them
 Secretes…
• Oxytocin: stimulates uterine contractions during
parturition and milk letdown from the mammary ducts
• Antidiuretic hormone (ADH): maintains water balance in
the body by increasing water reabsorption in the kidneys
Thyroid Gland
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Regulates metabolism, iodine uptake, and blood calcium levels
Located in the neck, contains two lobes, one on each side of
trachea
Can become overactive (hyperthyroid) or underactive (hypothyroid)
Only endocrine gland that can be palpated when enlarged
Produces and secretes…
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Triiodothyronine (T3) and Thyroxine (T4)
 Increases metabolic rate in tissues (increases oxygen consumption)
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Increases heart rate
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Makes heart more sensitive to epinephrine
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Stimulates the breakdown of adipose tissue
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Stimulates erythropoiesis
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Necessary for normal growth and development
Calcitonin: promotes the absorption of calcium from blood into bones
Thyroid Gland
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Butterfly shaped gland
HORMONES SECRETED BY THE THYROID GLAND
Hormone
Function
Thyroxine (T4)
Metabolism
Triiodothyrodine (T3)
ATP generation
Oxygen consumption
Calcitonin
Ca metabolism
Parathyroid Glands
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Four glands located on the surface of the thyroid
gland

Produces and secretes…

Parathormone (parathyroid hormone-PTH)
 Increases
blood calcium levels by reducing bone
calcium levels (calcium is regulated in the body by the
antagonistic actions of PTH and calcitonin.
 Regulates
phosphorus content of blood and bones
Adrenal Glands

Located cranial to the kidneys

Regulate electrolytes, metabolism, sexual functions and the bodies
response to injury
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Consist of 2 parts
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Adrenal cortex

Adrenal medulla
Adrenal Glands - Adrenal Cortex
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Hormones classified as steroids
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Produces and secretes corticosteroids…
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Mineralcorticoids: regulate electrolyte and water balance by affecting ion
transport in the kidney. Aldosterone (is the principal mineralcorticoid) which
regulates sodium and potassium.
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Glucocorticoids: regulate carbohydrate, fat and protein metabolism; resistance
to stress; and immunologic functioning. Example is hydrocortisone (cortisol)
which converts fat and protein into glucose, increasing blood sugar.
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Androgens: aid in the development and maintenance of male sex characteristics.
Example is testosterone which increases strength and muscle mass.
Adrenal Glands – Adrenal
Medulla

Produces and secretes…
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Epinephrine (adrenaline): stimulates the sympathetic
nervous system (flight or flight system) and increases
blood pressure, heart rate, and blood glucose.

Norepineherine (noradrenaline): stimulates the
sympathetic nervous system and increases blood pressure,
heart rate, and blood glucose.
Thymus
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Gland that operates in young animals
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Located near midline in the cranioventral portion of the thoracic cavity.
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Immunologic function through its role in the maturation of t-lymphocytes

Produces and secretes...
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Thymosin: promotes full development of T-lymphocytes
Pancreas
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Located near the proximal duodenum
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Has both endocrine and exocrine functions

Produces and secretes…
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Insulin: decreases blood glucose levels by transporting
blood glucose into body cells or into storage as glycogen
(main carbohydrate)

Glucagon: increases blood glucose levels by breaking down
glycogen
Pineal Gland
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Located in the central portion of the brain
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Functions are not fully understood but has to do with
circadian rhythm (events occurring in a 24-hour period)

Produces and secretes…
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Melatonin: controls circadian rhythm and plays a role in
sleep, behavior, coat growth, seasonal rituals, aging and
reproduction
Gonads
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Associated with reproduction
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Ovaries in females and testes in males

Produces gametes (sex cell)

Ovaries secrete…
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Estrogen: aids in the development of secondary sex characteristics (example is
mammary gland development) and regulates ovulation

Progesterone: aids in the maintenance of pregnancy, also secreted from the
corpus luteum and placenta.
Testes secrete…
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Testosterone: increases the development of secondary sex characteristics
(example is horn growth in rams, shoulder girth in cattle and horses). It is
thought to also be secreted from ovaries and adrenal cortex but in very small
amounts.
HORMONES SECRETED BY THE GONADS
Organ
Hormone
Function
Ovary
Estrogen
Heat cycle
Progesterone
Pregnancy
Inhibin
Inhibit FSH
Testes
Testosterone
Libido
Uterus
Prostiglandins
Luteolytic
Equine Chorionic
Gonadotropin (ECG)
Accessory Corpus Luteum
Relaxin
Relaxes uterine/cervical
muscles in preparation for
parturition
Summary:
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