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Isfahan University of Technology
College of Agriculture, Department of Animal Science
Advanced Reproduction
Physiology
(Lecture 1)
Prepared by: A. Riasi
http://riasi.iut.ac.ir
The syllabuses

Puberty and sexual maturity

Physiology of gamete production

Hormonal & non-hormonal secretions of reproductive
in male and female animals

Physiology of pregnancy and embryo development
The syllabuses

Physiology of parturition

Pheromones

Abnormality of reproduction

Reproductive immunology

Recent
advance
physiology
associated
with
reproductive
References
1.
Reproductive in Farm Animals, By: E.S.E. Hafez
2.
Reproduction in Dairy Cattle 1&2, By: Gietema
3.
Improving the Reproductive Management of Dairy
Cattle Subjected to Artificial Insemination, By: IAEATECDOC-1533
4.
Review and Original Papers
Puberty and sexual maturity

Puberty is originated from Latin word “pubscere”

Hypothalamus control puberty in animals

Two centers in hypothalamus:

Tonic center

Surge center
Puberty
Surge
Surge
Tonic
Tonic
Puberty

In near to puberty age:
 Sensitivity of the hypothalamic tonic center
 GnRH and gonadotrophins secretion
 Sensitivity of GnRH surge center in hypothalamus
Puberty
Puberty
Effect of testosterone on male brain
T
T
E2
Surge Center
Does not
Develop
Testis
Blood Brain
Barrier
Effect of estrogen on female brain
aFP + E2
E2
Placenta
E2
E2
E2
Ovary
Blood Brain
Barrier
Surge Center
Develops
Factors affecting puberty

Puberty may affected by different factors:

Heritability

Environmental factors

Birth month

Social condition

Nutritional factors

Age and weight
Role of leptin in puberty

Effect of a minimum percentage of body fat

Serum leptin concentrations

Leptin does not serve as triggering signal but acts
mainly as a permissive signal that permits puberty to
occur.
Role of leptin on puberty
Physiology of Testicular Function
Functional organization of testis

The testes have two compartments:

Tubular compartment (tubuli seminiferi)

Interstitial compartment (interstitum)
Functional organization of testis

The interstitial compartment:

The leydig cells

Secretion of testicular testosterone

Secretion of insulin like factor 3 (INSL3)

Immune cells

Blood and lymph vessels

Nerves

Fibroblasts

Loose connective tissue
Functional organization of testis

Different type of leydig cells (Ge and Hardy, 2007):

Stem Leydig cells as founder cell

Progenitor Leydig cells as a committed stem cell

Fetal Leydig cells as a terminally differentiated cell in the
fetus

Adult Leydig cells as the terminally differentiated Leydig
cell
Functional organization of testis

The interstitial compartment also contains cells
belonging to the immune system:


Macrophages, probably influence the function of leydig cells:

Proliferation

Differentiation

Steroid production
Lymphocytes
Functional organization of testis
Immunological compartments of the
testis. Sertoli cells (S) traverse the
testicular tubules, keeping in close
contact with the germ cells. Together
with the peritubular cells, they form the
seminiferous epithelium. The blood–
testis barrier (tight junctions) is built by
tight junctions between neighboring S,
dividing the seminiferous tubules into a
basal and adluminal compartment. The
interstitial space contains the Leydig
cells (L) and the immune cells such as
macrophages (MP), dendritic cells (D),
mast cells (M), and T cells as well as
blood vessels (BV) with migrating
leukocytes
Functional organization of testis

Spermatogenesis
takes
compartment:

Germ cells

Somatic cells

The peritubular cells

Sertoli cells
place
in
the
tubular
Functional organization of testis

Peritubular cells produce several factors that are
involved in cellular contractility (Holstein et al. 1996):

Panactin

Desmin

Gelsolin

Smooth muscle myosin and actin
Functional organization of testis

Several regulators of cell contractions are reported:

Oxytocin

Oxytocin-like substances

Prostaglandins

Androgenic steroids

Endothelins

Endothelin converting enzymes

Endothelin receptors
Functional organization of testis

These cells also secrete extracellular matrix and factors
typically expressed by connective tissue cells:

Collagen

Laminin

Vimentin

Fibronectin

Growth factors

Fibroblast
Functional organization of testis

Sertoli cells synthesize and secrete a large variety of
factors:

Proteins

Cytokines

Growth factors

Opioids

Steroids

Prostaglandins

Modulators of cell division
Functional organization of testis

The Cytoplasm of sertoli cells contains:

Eendoplasmic reticulum

Smooth type

Rough type

A Prominent Golgi apparatus

Lysosomal granules

Microtubuli and intermediate filaments
Functional organization of testis

Another important functions of Sertoli cells:

Final testicular volume

Sperm production
Hormonal control of testicular function
Hormonal control of testicular function

Pituitary gonadotropes are the central structure
controlling gonadal function.

In
turn,
are
regulated
by
the
hypothalamic
gonadotropin-releasing hormone (GnRH).

GnRH secretion depends on the activation of the
GPR54 receptor.
Hormonal control of testicular function

GnRH receptors are located on the surface of the
GnRH neurons and stimulated by the peptide
kisspeptin.

The pituitary function is also under the control of
gonadal steroids and peptides that influence its activity
both directly and through the hypothalamus.
Hormonal control of testicular function

The
Gonadotropin-producing
cells
constitute
approximately 15% of the adenohypophyseal cell.

The same cell type is believed to secrete both
gonadotropins.

Pituitary gonadotropes are often found in close
connection with prolactin cells.
Hormonal control of testicular function

Dramatic changes by pubertal activation:

The proximity of several stimulated endocrine cells types to
each other and to the germinal cell line.

Central feedback actions:

FSH

LH

Testosterone
Hormonal control of testicular function

In male testosterone is major the hormone controlling
GnRH secretion

Testosterone can act as such or after metabolism to
DHT or estradiol.
Hormonal control of spermatogenesis

During
spermatogenesis
gonadotropes
regulate
testicular function.

Testosterone and FSH affect the seminiferous tubules
and enhance spermatogenesis

LH affect the release of sperm from germinal
epithelium (spermiation)
Hormonal control of testicular function

High concentration of testosterone may find in
seminiferous tubules, rete testis, afferent tubules and
epydidymis.

Effect of inhibin and activin on FSH secretion and
spermatogenesis
Hormonal control of testicular function

The other hormones may affect testicular funtion:

Prolactin

GH and IGF-I

Insulin

Glucocorticoids

Thyroid hormones

PGE2

Testicular GnRH
Testicular androgens

Androgens are essential for:

The development and function of testes

Maturation of secondary sexual characteristics

Masculinization of the bone-muscle apparatus

Libido

Stimulation of spermatogenesis
Testicular androgens

Physiological effects of androgens depend on different
factors:

Number of androgen molecules

Distribution of androgens and their metabolites inside the
cell

Interaction with the receptors

Polyglutamine number of the amino acid sequence in the
androgen receptor

Receptor activation
Testicular androgens

In turn, androgen concentrations in the blood depend
on:

The synthesis rate

Balanced by metabolic conversion and excretion.
Testicular androgens

The main site of androgen production in the testis is
the Leydig cell.

Since Leydig cells cannot store androgens, de novo
biosynthesis takes place continuously.

LH as the central regulatory factor controls both
steroidogenesis
and
homeostasis in vivo.
Leydig
cell
cholesterol
Testicular androgens
Testicular androgens

Cholesterol is stored in cytoplasmic lipid droplets.

The number of lipid droplets is inversely related to the
rate of androgen synthesis in the Leydig cell.
Testicular androgens

Testosterone moves from the leydig cells into:

Blood vessel

Lymphatic vessel

Seminiferous tubules
Testicular androgens

Testosterone also give rise to two other potent
androgens:

Dihydrotestosterone (DHT)

5α-androstandiol
Testicular androgens
Testicular androgens

Circulating testosterone is found in three forms

Free

Bounded with a liver-drived sex steroid-binding globulin
(SSBG)

Bounded with albumin and other proteins
Testicular androgens

Testosterone is excreted by urine:

As glucronide (1% of daily production of testosterone)

17-ketosteroids products
Testicular androgens
Testosterone (T) is synthesized in the testis. After entering the target cells (in the
hypothalamus, pituitary, testis and wolffian duct) T is directly bound to the androgen
receptor (AR) and the complex T-AR binds to specific DNA sequences and regulates gene
transcription, which can result different works.
Testicular androgens
Specific actions of Dihydrotestosterone (DHT). After entering the T to target cells (in the urogenital
sinus, urogenital tubercle, and several additional androgen target tissues) T is metablized to 5αDihydrotestosterone (DHT) by the enzyme 5α-Reductase type 2. DHT binds directly to the androgen
receptor (AR) and the complex DHT-AR interacts to specific DNA sequences and regulates gene
transcription, which can result in differentiation and development of the prostate, the external genitalia
and at puberty in several secondary male characteristics.
Testicular androgens
Testicular androgens

The major role of testosterone:

Stimulates of differentiation of the wolffian ducts into the
epididymis, vas deferens and seminal vesicles.

With or without DHT causes enlargement of the penis and
seminal vesicles.

Causes enlargement of the larynx and thickening of the
vocal cords.
Testicular androgens

The major role of testosterone:

Local hormone required for initiation and maintenance of
spermatogenesis.

Cessation of linear growth by closure of the epiphyseal
growth center.

Enlargement of the muscle mass during puberty.

Important effect on lipid metabolism.
Testicular androgens

The major role of testosterone:

Initiation of sexual drive.

Suppression of mammary gland growth.

Stimulation hematopoiesis.

Stimulation of renal sodium reabsorption.

Stimulation of aggressive behavior

Suppression of hepatic synthesis of SSBG, cortisol-binding
globulin and thyroxin-binding globulin.
Testicular androgens

The major role of DHT and 5α-androstandiol:

DHT is specifically required in the fetus for differentiation
of the genital tubercle, genital swellings, genital folds and
urogenital sinus into penis, scrotum, penile urethra and
prostate respectively.

DHT is required during puberty for growth of scrotum and
prostate and stimulation of prostatic secretion.
Testicular androgens

The major role of DHT and 5α-androstandiol:

DHT and 5α-androstandiol stimulate the hair follicles.

DHT and 5α-androstandiol increase production of sebum.

DHT influence the spermatogenesis.
Semen properties

Semen volume is controlled by different factors:

Animal species

Breed

Individual properties

Season of year

Semen collection time
Semen properties
Sperm collection times for different animals
Livestock
Number of Collections
Bull
Two times per week
Ram
Daily for weeks
Boar
Two times per week
Stallion
Natural - two times per day
Artificial - every other day
Rooster
Daily
Semen properties

Semen liquid produced by:

Sertoli and rete testis

Genital tract secretions

Accessory glands secretion
Semen properties

Special proteins in semen liquid:

Androgen binding protein (ABP)

Acrosin inhibitor protein

Glycoproteins
Semen properties

Different ions in semen liquid

Na+

Cl-

K+

Ca++

Mg++

Hco3-
Semen properties

Other components in semen liquid:

Hormones

Vitamins

Lipids and fatty acids

Immunoglobulin A

Energy sources
Semen properties

Energy metabolism in sperm:

Fructose production by sorbitol dehydrogenase

Fructolysis

Role of membrane Plasmalogens
Semen properties

Factors may affect sperm metabolism rate:

Temperature

pH

Osmotic pressure

Sperm concentration

Hormones

Gases

Light
Some research papers associated to this lecture
1. Asadpour, R. et al. The effect of antioxidant supplementation in semen extenders
on semen quality and lipid peroxidation of chilled bull spermatozoa. Iranian
Journal of Veterinary Research, Shiraz University, 2012, 13: No. 3, Ser. No. 40.
2. Umut Tasdemir. et al. Effects of various cryoprotectants on bull sperm quality,
DNA integrity and oxidative stress parameters. Cryobiology xxx (2012) xxx–xxx.
3. Gaffari Tu¨rk. et al. Effects of pomegranate juice consumption on sperm quality,
spermatogenic cell density, antioxidant activity and testosterone level in male
rats. Clinical Nutrition, 2008, 27: 289-296.