chapter 3 spermatogenisis

autocrine signaling

cells respond to signaling substances that they themselves secrete cancer cells

androgen binding protein

receptors that bind to testosterone

testis

testes is made of seminiferous tubules, interstitial cells, blood vessels and extracellular material Spermatogenesis occurs in seminiferous tubules Spermatogenesis occurs from basement membrane towards the lumen of tubules. Reproduction and survival of sperm require temperature lower than normal core body temperature.

paracrine signaling

Signals coming from nearby cells

endocrine signaling

Signals that originate from a distance and are distributed via the circulation

path of sperm

Spermatogenesis, occurs in the testes after which the full formed sperm leave the seminiferous tubules to enter the epididymus where they remain stored until the appropriate moment. - preparation for ejaculation, the sperm following the route: - First leaves the epididymus to enter the vasa efferentia. The - sperm move along each vas efferens and enter the vas deferens - move along the vas deferens materials are added to the sperm and to the extracellular fluid (forming semen) that surrounds them. The prostate gland and seminal vesicles add fluid and nutrients at the time of sperm ejaculation providing most of the volume of the ejaculate. This complex of fluid and sperm cells travels up the urethra to be released externally to the male.

spermatogenisis signaling

The intimate relationship between the germ cells and Sertoli cells involves reciprocal paracrine interactions between these two cell types, and the overall coordination of spermatogenesis is orchestrated by endocrine interactions between the pituitary gland and the somatic cells of the testis.

midpiece of sperm

The middle region of the sperm mainly dominated by a spiral complex of mitochondria that are fused together. energy for swimming

testesosterone

The principal promoters of germ cell differentiation in male vertebrates are the androgens,Testosterone. The testosterone stimulates sperm maturation, controls growth, development, functioning and maintenance of sex organs. Also stimulates bone growth and protein anabolism.

pituitary gland

The production of testosterone by the interstitial cells is regulated by a gonadotropic hormone, called luteinizing hormone (LH) released by the pituitary gland into the circulation. Another gonadotropic hormone, follicule stimulating hormone (FSH), is also involved in regulation of spermiogenesis by acting directly on the Sertoli cells. - will release HGH

sperm cell

The ultimate goal of spermatogenesis is the production of spermatozoa or sperm cells.. There are three main regions in the sperm cells.

tail of sperm

This is essentially a flagellum with some specializations not seen in non-mammalian flagella

initial Events of spermatogenesis

- PGCs divide to form type A1 spermatogonia cells found adjacent to the outer membrane of the Seminiferous tubules - at maturity, they divide to make another A1 spermatogonium(self regenerating) as well as a second type , the type A2 spermatogonium - A2 spermatogonia divide to produce A3 spermatogonia, which then give the type A4 spermatogonia

sertoli cells within seminiferous tubles

- Surround developing sperm cells Synchronize the events of spermatogenesis (all stages are aligned) from outer membrane to lumen - Secrete critical proteins (e.g., growth factors, androgen-binding protein, inhibin) that are important for testes function and spermatogenesis Secretion of tubule fluid - Phagocytosis of residual bodies so cellular constituents can be recycled ·Separation of the circulatory system from luminal environment of tubules (blood-testis barrier) (protection from immune cells) - Tight junctions are formed between adjacent Sertoli cells, producing a difusion barrier, allowing the Sertoli cells to regulate the environment that bathes the germ cells

continued spermatogenisis

- Type B spermatogonia divide once to generate the primary spermatocytes, the cells that enter meiosis - Each primary spermatocyte undergoes the first meiotic division to yield a pair of secondary spermatocytes, which complete the second division of meiosis to form haploid cells called spermatids, which are still connected to one another through their cytoplasmic bridge.

Gonadotropin-releasing hormone (GnRH) hypothalamus

acts on pituitary gland Promotes secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH)

Sperm Cell Membrane:

contains receptors for recognizing the egg. Remember, all cells are completely surrounded by a cell membrane (sometimes called the plasma membrane

sex determination

during development body by default will form ovries but then the y chromosome gets activated will inhibit the continued formation of ovaries and initiate formation of male organs

nucleus of sperm

haploid, gametic nucleus will fuse with haploid egg nucleus forming 2N zygote nucleus

LH

luteinizing hormone acts on leydig cells Testosterone are synthesized by specialized somatic cells called the interstitial cells (cells of Leydig) which are located in the connective tissue between the seminiferous tubules.

what does the zygote recieve from egg

mitochondria

protamines

nucleus size of the sperm must be be compact so the nucleosome structureis altered where all of the histones are removed and replaced by protamines which allow DNA to pack more tightly - during fertilization protamines are removed and replaced by histones

spermatogonia

once PGCs reach the genital ridge and interact with somatic cells they become spermatogonia

centrioles

organize axoneme (microtubules) of the flagellum.

Gametogenisis: Females

process of formation of oocytes.. begins at embryonic stage and arrests and resumes at puberty continues until menopause - The first meiotic division starts before birth but fails to proceed. It is eventually completed about one month before ovulation in humans. In humans, the second meiotic division occurs just before the actual process of fertilization occurs.

Spermiogenesis

the differentiation of of spermatids to spermatozoa during spermatogenesis - golgi vesicles combine to form an acrosomal vesicle with all hydrolytic enzymes located near the nucleus - Centosomes start to organize microtubules into long flagella - Mitochondria start to localize next to the flagella to provide ready energy - The nucleus condenses in size and is stabilized by special proteins called protamines - The excess cytoplasm is pinched off as a residual body (no need for organelles and cytoplasmic proteins)

Gametogenisis in male

the spermatogonia enter meiosis and produce sperm from puberty until death. The process of sperm production takes only a few weeks. Each ejaculation has 100 to 500 million sperm.

head of sperm cell

: Front end where the haploid nucleus resides covered by a single membrane sac (bag) of enzymes (acrosome). A pair of centrioles lies just behind the sperm nucleus.

acrosome

A specialized lysosome containing digestive enzymes for penetration of the material surrounding the egg.

leydig cells

Also known as interstitial cells of Leydig, are found adjacent to the seminiferous tubules in the testis. They can secrete testosterone and are often closely related to nerves. Leydig cells have round vesicular nuclei and a granular eosinophilic cytoplasm.

Incomplete cytokinesis

During spermatogonial divisions cytokinesis is incomplete and there are cytoplasmic bridges between the cell

negative feedback inhibition

Inhibin, produced by Sertoli cells and inhibits FSH to stop spermatogenesis (feedback inhibition mechanism).

fate of A4 spermatogonia

It can form another A4 spermatogonium (self- reniewal) 2. It can undergo cell death (apoptosis) 3. It can differentiate into the first committed stem cell type, the intermediate spermatogonium. These cells divide mitotically once to form type B spermatogonia. Type B cells are the last cells of the line that undergo mitosis.

Sperm are tiny, but highly specialized missiles for delivering the male genome:

Microfilaments shoot the acrosome into the egg to 'harpoon it' and pull it in. The acrosome has enzymes for breaking into the egg. The midpiece has large numbers of mitochondria for horsepower. The tail has a powerful flagellum for driving the sperm into the proximity of the egg (in humans, through the uterus and up into the oviduct.

FSH

Acts on sertoli to create androgen recptors that bind to testosterone

what does the zygote receive from sperm

nucleus and centrioles

flagellum

whip-like "tail" of sperm functions in sperm motility; motive force for sperm involves sliding of axonemal microtubles as is typical for all flagella and cilia in all organisms that possess them. Mitochondria: provide energy (ATP) for sperm motility