The document summarizes key concepts about the regulation of reproduction through hormones and target tissues. It defines hormones and describes how they interact with target tissues. The hypothalamus controls reproduction by secreting hormones that signal the pituitary gland. The pituitary then secretes hormones like FSH, LH, and prolactin that target the gonads and other reproductive organs. These secondary hormones include estrogen, progesterone, and testosterone that regulate sexual development and function. The document outlines the hormones secreted at each level of the hypothalamic-pituitary-gonadal axis and their roles in the male and female reproductive cycles.

1. THER 608 Lecture # 4 & 5
Physiology of Reproduction
Regulation of Reproduction:
Nerves, Hormones and
Target Tissues
NS + ES = NE
1

2. Chronology of Changing Concepts on
Regulation of Reproduction
2
CNS
Neural
ES
Hormonal
HHPS
Neuroendo.
GF
Intragonadal

3. Definition of Hormone
“Hormone is a physiologic, organic,
chemical substances synthesized
secreted by ductless endocrine
glands which passes into
circulatory system for transport
and inhibits, stimulate or regulate
the functional activity of target
organs or tissues.”
Short half life
Act in minute quantities
Bind to specific receptors
Neurohormone (H by a Neuron)
3

4. Target Tissue Bind Hormones,
Other Tissues do Not
4

5. 5
EndocrineGlandsofthe
cow

6. Schematic Drawing of
Hypothalamic Nuclei and Pituitary
Nucleii controlling
Preovulatory LH & FSH
Nucleii controlling Tonic LH
& FSH
6

7. Terminology of the Subdivisions of
the Hypophysis (Pituitary)
Pituitary gland is located in the sella turcica,a bony depression at the base of the brain
7
Neurohypophysis
(Posterior
Pituitary)
Median
Eminence
Infundibulum
Infundibular
Stem
Neural Lobe Posterior Lobe
Adenohypophysis
(Anterior
Pituitary)
Pars Intermedia
Pars Tuberalis Anterior Lobe
Pars Distalis

8. Cell Types of Anterior Pituitary
• Somatotrophs (Growth Hormone, GH)
• Corticotropes (Adeno. Cor. Horm. ACTH)
• Mammotrops (Prolactin, PRL)
• Thyrotrops (Thyroid Stim. Horm. TSH)
• Gonadotrops (Follicle Stim. Horm. FSH,
Luteinizing Hormone, LH)
8
Pineal Gland (Epiphysis) – Neuroepithelial evagination from roof of
third ventricle under posterior end of corpus callosum.
Amphibians = Pineal is a Photoreceptor
Mammals = It is an endocrine gland
(Long days & Short days)

9. Anatomy of Hypothalamus and Pituitary
9

10. 10

11. Hormones can be classified by
their;
• Source
• Mode of action
– Releasing hormone, Gondotropins,
Pregnancy maintenance, metabolic,
luteolytic
• Biochemical classification
11

12. Biochemical Classification
• Proteins: Poly peptides, (FSH, LH & Oxytocin)
• Steroids: Cholesterol, (Testosterone, P4, E2)
• Fatty acids: Arachidonic acid, (Prostaglandins)
• Amines: tyrosine, (melatonin)
12

13. Functional Anatomy of Hypothalamus and Pituitary
• Hypothalamus. Neural control center for
Reproductive hormones . It Occupies very small
portion of the brain. Consists of region of third
ventricle, extending from the optic chiasma to
mammillary body.
–Neural connections (Hypo - Post pit)
–Vascular connections (Hypo - Ant pit) 13

14. Hypoth. Hypoph. Port. System
• Arterial blood enter AP via Superior and inferior
hypophseal artery. The superior hypo artery forms a
capillary loops (Primary Portal Plexus) at the ME
and Pars Nervosa. Blood from these caps then
enter into veins which then reenter into another loop
(Secondary Portal Plexus) of caps at the anterior
pituitary level. From here the blood is sent back to
the hypothalmus (retrograde fllow) and some go to
the venous system. Therefore, in this system
blood begins and ends in caps without going into
the heart. This type of system is called as short loop
feedback. 14

15. Hypothalamo-Hypophseal Portal System
15
Post lobe does
not have portal
system

16. 16
Hypothalamo-
HypophsealPortal
System

17. Mechanism of Action of Hormones
Steroid Hormone
eg., P4 - LH
Protein Hormone
eg., FSH – E2
•Receptors for protein hormone present on the
cell surface.
•Hormone receptor binding
•Adenylate cyclase activation
•Protein kinase activation
•Synthesis of new product
• no receptors on cell surface
•Steroid transport via diffusion into cell
membrane and cytoplasm
•Binding of steroid to nuclear
receptors.
•Messenger RNA synthesis and protein
synthesis
17

18. SteroidHormone
MechanismofAction
18

19. ProteinHormones
MechanismofAction
19

20. Modes of Intercellular
Communication
• Neural
Neurotransmitters are released at synaptic junctions
• Endocrine
Hormone transported through blood circulation
• Paracrine
Products of cells diffuse through extra cellular fluids
and effect the neighboring cells
• Autocrine
Cells secrete chemical messengers that binds to the
receptors on the same cells that secrete them 20

21. Modes of Intercellular
Communication
21

22. Regulation of Hormone Secretion
Negative Feedback (Inhibitory) Suppression of
GnRH neurons
• Involves two or more glands
• A change in opposite direction of initial change
• Primary mechanism maintaining homeostasis
• eg., FSH and Estradiol
Positive Feedback (Stimulatory) Stimualtion of
GnRH neurons
• Change in same direction of initial change
• Not used to maintain homeostasis
• Important in certain physiological circumstances eg.,
Childbirth, "fight or flight" responses, Ovulation, etc. 22

23. Neural and Neuroendocrine Reflex
• Neuroendocrine reflex: Sensory neurons –
afferent neurons (towards spinal cord) – spinal
cord – synapse – efferent neurons (leaving spinal
cord)– resultantly hypothalamus releases neuro
hormone which effects the target tissues
Example: Milk Ejection Reflex: Stimuli (suckling of
teats/ udder stimulation), Neurohormone (oxytocin)
• Neural reflex
23
Interneurons
Neurotransmitter
Excitatory or Inhibitory

24. Simple Neural and Neuroendocrine reflex
24

25. 25
StepsofSimpleneuraland
Neuroendocrinereflex

26. BiosynthesisofSteroid
HormonesFromCholesterol:
Simpleview
26
27 carbons
21 carbons
21 carbons
19 carbons
18 carbons
Enzyme conv.
Enzyme conv.
Enzyme conv.
Enzyme conv.

27. Summary of Hypothalamic Regulating
Reproduction
27
Hormone Origin/ Nucleii Principal Function
Prolactin inhibiting
hormone
Prolactin releasing
hormone
Hypothalamus Inhibits prolactin release
Stimulates prolactin release
Gonadotropin
releasing hormone
(GnRH)
VMN
AC
ME
Stimulates tonic release of FSH
Gonadotropin
releasing hormone
AHA
POA
SCN
Stimulates preovulatory surge of
FSH, LH
Oxytocin PVN
SON
Induces uterine contraction, milk let
down
Melatonin Pineal Inhibits gonadotropic activity in long
day breeders eg., hamster
Stimualte gonadotropic activity in short
day breeders eg., sheep

28. Summary of Reproductive Hormones Secreted
by the Pituitary
28
Hormone Structure
and source
Principal Function
Follicle
Stimulating
Hormone
Glycoprotein Stimualtes follicle growth in
females and spermatogenis in
male
Luteinizing
Hormone
Glycoprotein Stimulates ovulation and
luteinization of follicles/CL in
females and Testosterone
secretion in male
Prolactin Protein Promtes lactation and maternal
behavior
Oxytocin Protein,
stored in
posterior
lobe
Stimulates contractions of
pregnant uterus, causes milk
ejection

29. Summary of Hormones Secreted by
Reproductive Organs
29
Hormone Structure &
Source
Principal Function
Estrogen 18 C, steroid, theca
interna of follicle
Sex behavior, stimulates
development of secondary sex char.
Progesterone 21 C, Steroid, CL Preparing uterus for implantation,
pregnancy maintenance
Testosterone 19 C, Steroid, LC Spermatogensis, dev. of sex glands
Relaxin Polypeptide, CL Cervical dilation, uterine contraction
PGF 20 C Unsat Fatty acid,
all body tissue esp.
endometrium
Luteolysis, uterine contraction
Activin Protein, follicular fluid,
rete testis
Stimulates FSH secretion
Inhibin Protein, found in Sertoli
cells, granulosa cells
Inhibits FSH release

30. Summary of Hormones Secreted by Placenta
30
Hormone Species Principal Function
Human chorion
gonadotropin
(primates only) hCG
Human,
monkey
LH activity, maintain CL
Equine chorion
gonad. (eCG/PMSG)
Horse FSH activity, accessory CL
formation
Estrogen Sheep, Cattle Sexual Behavior
Progesterone Sheep, Cattle Pregnancy maintenance
Placental Lactogen Sheep, Cattle Regulates transport of
nutrients from dam to fetus
Pregnancy protein
B
Sheep, Cattle Maternal recognition

31. Prostaglandins
20 carbon unsaturated fatty acid (arachidonic acid)
• Secreted by all body tissues especially endometrium
• Cause regression of CL. This help in the control of
estrous cycle (estrus synchronization)
• in reproductive and GI tract Contraction of smooth
muscles
• Regulate several other phenomena eg., erection, sperm
transport, ovulation, parturition etc.,
31

32. Summary of REPRODUCTIVE
HORMONES
Name of
Hormon
e
Bio. Class. Source Male
Target
tissue
Female
Target
Tissue
Male
Primary
Action
Female
primary
action
GnRH Neuropepti
de
Hypothala
mic surge
and tonic
Center
Ant Lobe Ant Lobe Release of
FSH, LH
Release of
FSH, LH
LH Glycoprotein Ant Lobe Testis
(Leydig
cells)
Ovary (cells
of theca
interna and
luteal cells
Stimulate T
production
Ovulation,
formation
of CL and P4
secretion
32