Dairy Cattle Breeding & Selection

Reproduction

“Endocrinology”

Topic Objectives:

1. Describe the inter-relationship between the Endocrine system and the Nervous system.

2. Describe the origin and function of the major hormones involved with reproduction.

I. Introduction

A. Look at the two systems.

1. Endocrine System a. Causes slower and longer lasting changes

within the body. b. Examples:

1) Growth2) Reproduction3) Lactation4) Secondary Sex Characteristics

2. Nervous System a. Causes rapid changes and/or adjustments

within the body. b. Examples:

1) Immediate reaction to any kind of stress such as: a) Pain b) Fear c) Heat d) Exertion e) Etc.

B. The two systems work together as one system.

1. Called the Neuroendocrine System. a. Referred to this way because of the

overlapping effect each system has on the other. b. Example: Adrenaline will cover up the

effects of oxytocin.

C. Definitions to Know

1. Hormone: Chemicals synthesized from the endocrine glands that influence activities of other organs within the body. Example: The ovary produces estrogen, progesterone, and

relaxin, all of which affect the body in different ways. 2. Neurohormone: Chemicals synthesized in the

central nervous system (or in the neuron; nerve cell) that influence activities of other organs within the body. Example: FSH, LH (both produced in the anterior pituitary

gland) and Oxytocin (produced in the posterior pituitary gland).

3. Neuroendocrine System: A combination of the endocrine system and the central nervous system working harmoniously.

II. Hormone Secretions in the Female are brought about in

two ways.

A. External Affects (Conditions occurring outside the body: i.e.: Environment) 1. Temperature changes: Extreme heat for

example will cause the blood to circulate faster. 2. Improper handling of cattle causes the system

to speed up due to adrenaline secretions. B. Internal Affect (Conditions occurring

inside the body: i.e.: Estrous Cycle)

III. Classifications of Glands

A. Endocrine

1. Internal ductless glands that discharge their secretions directly into the blood stream which then transports them to their place of action.

2. Secretion is a hormone that may also be called a chemical messenger.

3. Their job is to activate or bring about a change in the body.

4. Hormones have two main purposes: a. Excitatory: Activates an organ to do

something. b. Inhibitory: To inhibit or stop something from

functioning.

5. There are two major groups of Endocrine organs based on the type of secretion. a. Only Hormones and not other enzymes or

substances produced and released in the body:1) Examples:

a) Thyroid b) Parathyroid c) Pituitary d) Adrenals e) Pineal f) Thymus

b. Hormones and other enzymes or substances produced and released into the body:1) Example

a) Pancreas – Insulin b) Testes – Spermatozoa – Testosterone c) Ovary – Egg – Progesterone, Estrogen d) Stomach – Gastric Juice & Enzymes e) Intestine – Digestive Enzymes

B. Exocrine Glands

1. Glands that discharge their secretions by ducts to various parts of the body or to the outside of the body. a. Mammary System b. Urinary System c. Sweat Glands d. Etc.

IV. Overview of the Endocrine and Central Nervous Systems

A. Both coordinate body functions and in many cases it takes both to perform the functions of reproduction.B. In general the secretions (Neurohormones) from the Central Nervous System stimulate the Endocrine Glands into actions sot hey will secrete their hormones…FSH, LH, Etc.

C. Basic function of the Central Nervous System is to control rapid adjustments of body to changes in the environment…Stress=Adrenalin Release.

D. Basic function of the Endocrine System is to regulate body changes more slowly…Growth, Lactation, Reproduction, etc.

V. Four Main Parts of the Nervous System

A. Brain – Control Center B. Spinal Cord – carries messages or

neurohormone to and from various parts of the body.

C. Peripheral Nervous System – Voluntary – All nerve cells outside the brain and spinal cord…except those nerves controlling the visceral organs (heart, stomach, etc.) 1. These nerves are routes of communication

between the central nervous system and the internal and external environment. (Afferent and Efferent Nerves)a. Afferent (Sensory) nerves – to the spinal cord.b. Efferent (Motor) nerves – to the reactor organ or

muscle.

D. Autonomic Nervous System – Involuntary and acts automatically: Controls the Visceral organs. (Stress the system and the neurohormone “Epinephrine/Adrenalin” inhibits milk let down as it blocks oxytocin). Includes two systems: 1. Sympathetic: This system tends to decrease

secretion and constrict blood flow. 2. Parasympathetic: Antagonistic System tends

to induce secretion and dilation blood vessels.

VI. Neuron

A. Basic cell of the Central Nervous System is the neuron.

B. Contains the following: 1. Cell Body: Control center. 2. Axon: Terminals that conduct impulses away

from the cell body. 3. Dendrites: Terminals that conduct impulses

to the cell body.

C. Nerve Impulses travel over one or more nerve cells to the spinal cord to the brain and then back to an effector organ such as a gland or muscle. The impulse may not always go to the brain before going to the effector organ.

VII. Brain

A. Composed of Four parts: 1. Cerebrum: Includes the Pituitary and

Hypothalamus.a. This is the largest part of the brain.b. Center or reasoning, thinking and voluntary muscle

control.c. Registers various sense…sight, smell, hearing.

B. Cerebellum 1. Coordinates such activities as eating, walking.

C. Pons 1. Coordinates breathing, swallowing,

rumination.

D. Medulla Oblongata 1. Works in cooperation with the Pons.

VIII. Spinal Column

A. A caudal extension of the Medulla Oblongata.

B. Delivers messages to and from the brain. C. Afferent nerves carry messages from

parts of the body to the spinal cord. D. Efferent Nerves carry messages from the

spinal cord of parts of the body.

IX. Miscellaneous: Hormones may have two or more purposes

to the system.

A. Oxytocin for example: 1. Initiates Milk Let-Down and also 2. Causes Uterine contraction during Estrus and

also 3. During Parturition

X. Location and Function of the Neuroendocrine Glands

A. Anterior Pituitary 1. Base of the Brain 2. Secretes Gonadotropins:

a. F.S.H. (Follicle Stimulating Hormone) to stimulate the ovary to produce an egg.

b. L.H. (Luteinizing Hormone) to cause the follicle to rupture and release the egg.

c. I.C.S.H. (in the male…Interstitial Cell Stimulating Hormone) to stimulate the interstitial cells to produce and release testosterone.

d. Also produces the following: 1) Prolactin – Lactogenic Hormone ( Milk). 2) G.H. – Growth Hormone 3) T.S.H. – Thyroid Stimulating Hormone – induces the thyroid to

take iodine from the blood for normal thyroid function. 4) A.C.T.H. – Adrenocorticortropic Hormone (Stress hormone –

causes the system to speed up…also one of the steroid type of chemicals).

B. Posterior Pituitary

1. Base of the brain 2. Secretes the following neurohormones:

a. Ocytocin – responsible for milk letdown and reproductive contractions.

b. A.D.H. – Antidiuretic Hormone: Control urine collection in the bladder and fluid concentration in the kidney. (Also water balance in tissue.)

C. Hypothalamus

1. Just in front of the Anterior Pituitary and the Cerebrum.

2. Regulates secretions of the Anterior Pituitary. 3. Produces Releasing Hormones (H) or factors (F):

a. Gonadotropin Releasing Hormone (GnRH) b. GRF – Stimulates GH release. c. Somatostatin – Inhibits GH release d. TRH – Stimulates TSH (also prolactin and GH) release e. CRF – Stimulates ACTH release. f. Prolactin Inhibiting Factor (Inhibits Prolactin release).

D. Thyroid

1. Two lobes located on each side of the Trachea just below the Larynx.

2. The Thyroid needs iodine to function properly and if not the thyroid keeps getting larger (Goiter).

3. Its secretions affect indirectly almost all of the body functions:

a. Carbohydrate and Protein Synthesis b. Utilization of Oxygen c. Milk Production d. Secretes Thyroxine, Triiodothyronine and Calcitonin e. In general…it affects the metabolism which the system operates; i.e.: a

dry cow compared to a cow milking heavy in her 2nd month of her lactation.

E. Parathyroid

1. Located just below the Thyroid 2. Produces Parathyroid hormone that is

necessary for the synthesis and utilization of Calcium and Phosphorus.

F. Pancreas

1. Located on the small intestine. 2. Secretes Digestive Enzymes

a. Insulin – Breaks down sugars. b. Glucagon – breaks down starch to glucose.

G. Adrenal

1. Located near the kidneys 2. Two glands:

a. Adrenal Cortex – 29 known functions: primarily it maintains mineral balance in the blood and fluids in the tissue. 1) Produces:

a) Glucocorticoids b) Mineralocorticoids

b. Adrenal Medulla – Secretes neurohormones…Epinephrine and Norepinephrine: in short this is Adrenalin. (Without this to help fight stress the animal would die…necessary to speed up the heartbeat, etc…(Fight or Flight Hormone)).

I. Ovary (Female)

1. Reproductive Organ of the Female that: a. Produces Estrogen (Estradiol) from its

Graffian Follicles. b. Produces Progesterone from its Corpus

Luteum. c. Produces Relaxin. d. Produces Inhibin – that inhibits FSH.

I. Testes (Male)

1. Interstitial Cells produce Testosterone. 2. Seminiferous Tabules produce

spermatozoa.

J. Placenta

1. The main two hormones produced. a. Estrogen b. Progesterone

2. Also produces Placental lactogen.

THE END