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Anatomy & Physiology-CH 17- The Reproductive System

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The Reproductive System
Essentially not required for the survival of an animal but required for the survival for the species. The process begins with fertilization. The spermatozoon must penetrate into the cytoplasm of the ovum. The fertilized ovum must then have a hospitable place to grow and develop. Ovum and sperm produced through a process called Meiosis- ensures the genetic make-up of each animal is unique.
Chromosomes
Coiled mass of DNA in the nuclei of cells containing genetic material. Each cell in an animal's body(except spermatozoa or ova) contains identical chromosomes, serves as a blueprint for all structures and functions
Chromosomes: Diploid Chromosome Number
Total number of chromosomes in the nucleus of each cell is the same (except for reproductive cells). Always an even number- chromosomes occur in pairs. The same across species lines.
Sex Chromosomes
Designed as either "X" chromosomes or "Y" chromosomes. If both of the sex chromosomes are X the individual is genetically female. If one is an X and the other is a Y the individual is genetically male.
Mitosis
Most body cells divide after the cell first makes a duplicate copy of its chromosomes. During the S Phase (synthesis) of interphase DNA replication occurs. A new second double helix is formed. During mitosis when the cell splits the one new daughter cell will take a helix and the other daughter cell will take the other helix. Genetic makeup of the two daughter cells is exactly the same as each other and as the parent cell.
Meiosis- Cell Division of Sex Cells
Chromosomes do not produce duplicate copies of themselves before daughter cells divide. Half of the total chromosomes (one from each diploid chromosomes pair and one sex chromosomes) go to each daughter cell. Only one pair goes the daughter cell. During fertilization one pair from the ovum and one pair from the sperm come together. Which chromosomes go to which daughter cell is entirely random.
Haploid Chromosome Number
Reduction Division- total number of chromosomes in each of the daughter cells is reduced to half the number of the parent cell. Ensures that the fertilized ovum from the union of spermatozoa and the ova has diploid number. Haploid chromosome number in the reproductive cells results from meiosis.
Spermatogenesis
Production of male sex cells. Occurs in seminiferous tubules of the testes. Produced continuously and in vary large numbers. Primarily spermatocyte (diploid number) divides by meiosis into secondary spermatocytes-haploid number. The secondary spermatocytes divide by mitosis into four spermatids. Spermatids grow tails and undergo other physical changes that convert them to spermatozoa. When the spermatozoa are fully developed they detach and are carried to the epididymis for storage before ejaculation. Half of the spermatozoa produced have an X sex chromosome and half have a Y sex chromosome.
Oogenesis
Production of female sex cells. Occurs in ovarian follicles. Female has fixed number of primary oocytes at or soon after birth. Produces small numbers of ova at a time. Each ovarian cycle produces one or more ova depending on the species. When recruited the primary oocyte divides by meiosis into a large secondary oocyte and a small "Polar Body". Polar bodies are not needed/used. Each has the haploid chromosome number. Secondary oocyte and the first polar body divide by mitosis into an ovum and three polar bodies.
Male reproductive System
Produces male sex hormones. Develops spermatozoa. Deliver the spermatozoa to the female system at the appropriate time.
Testes
Male Gonads. Produce sperm (spermatogenesis) and hormones. Interstitial cells located between the seminiferous tubules produce testosterone. Located outside the abdomen in the inguinal region. Housed in a sac of skin- the scrotum.
Spermatozoa Structure
Long , thin with 3 parts.
Spermatozoa Structure: Head
Contains nucleus of the cell. Covered by the Acrosome; contains digestive enzymes that help the spermatozoon penetrate the ovum.
Spermatozoa Structure: Midpiece
Power house of the cell. Large concentration of mitochondria arranged in a spinal pattern.
Spermatozoa Structure: Tail
Contains muscle-like contractile fibrils. Produces a whip-like movement of the tail and propels the cell forward.
Development of testes
Begins in the abdomen. Testes gradually pulled caudally and ventrally as the embryo grows.
Development of Testes: Gubernaculum
Band of connective tissue that attaches testes to scrotum.
Development of Testes: Inguinal Rings
Openings in abdominal muscles through which testes descend. At or soon after birth the testes are pulled down through this ring into the scrotum. Slit-like openings in the abdominal muscles.
Scrotum
Sac of skin that houses the testes. Helps regulate temperature of testes. Testes must be kept slightly cooler than body temperature in order to produce spermatozoa.
Scrotum: Cremaster Muscle
Passes down through the inguinal ring and attaches to the scrotum. Adjusts the position of the testes relative to the body depending on temperature. In warm temperature it relaxes and lets the testes hang down away from the body. In cold temperatures it pulls the testes closer to the body.
Spermatic Cords
Tube like connective tissue that contains blood and lymphatic vessels, nerves and the vas deferens. Forms a heat exchange mechanism that keeps the testes cooler than the rest of the body. Single testicular artery brings blood to the testes.
Spermatic Cords: Pampiniform Plexus
Meshwork of veins that surrounds testicular artery. Maintains testes at a temperature slightly lower the body temperature. Cools blood coming in from the testicular artery. Warms blood back to body temperature before it returns to the abdomen.
Tunics
Connective tissue that forms sheath-like layers around the testes and the spermatic cord. Derived from layers of peritoneum that were pushed ahead of the testes as they descended through the inguinal ring.
Tunics: Visceral Vaginal Tunic
Very thin inner layer, layer in direct contact with testes.
Tunic: Parietal Vaginal Tunic
Think outer layer. Forms a fibrous sac around each testis and spermatic cord.
Tunic: Tunica Albuginea
Fibrous connective tissue capsule surrounding each testis beneath the tunics.
Seminiferous Tubules
Site of spermatogenesis. Long convoluted U-shaped tube attached at both ends to system of ducts (rete testis).
Seminiferous Tubules: Interstitial Cells
Endocrine cells between the seminiferous tubules. Produce androgens (testosterone) under the influence of LH.
Seminiferous Tubules: Sertoli Cells
Support developing spermatids. "Nurse Cells". Also produce small amounts of estrogen.
Duct System
After detaching from Sertoli Cells, spermatozoa enter the rete testis. Then flow through the efferent ducts to the epididymis. Single long convoluted tube that connects the efferent ducts of the testis with the vas deferens. Storage and maturation of spermatozoa. Flat ribbon like structure attached along the surface of testis.
Epididymis
Has three regions. Head, body and tail.
Epididymis: Head
Site where spermatozoa enter from efferent ducts.
Epididymis: Body
Lies along surface of testis.
Epididymis: Tail
Continues on as the vas deferens.
Vas Deferens
AKA- Ductus deferens; part of the spermatic cord. Carries sperm from the epididymis to the urethra during ejaculation. Passes through inguinal ring then separates from spermatic cord and connects with urethra. Thick smooth muscle walls. Functions to propel sperm quickly from epididymis to urethra at time of ejaculation.
Vas Deferens: Ampulla
Enlargement of the vas deferens just before it joins the urethra found in some species. Contain glands that contribute material to semen.
Urethra
Pelvic Portion- entry point of vas deferens and accessory reproductive glands. Penile Portion- Runs down the length of the penis. Spermatozoa from vas deferens and secretions from accessory reproductive glands enter urethra and are pumped out as semen. Carries urine from the urinary bladder outside the body, urine flow temporarily blocked when ejaculation occurs.
Accessory Reproductive Glands
Secretes substances that make up semen. Ducts of all accessory reproductive glands enter pelvic portion of the urethra. Different species have different combinations of accessory reproductive glands. Produce alkaline fluid that helps counteract the acidity of the female reproductive tract.
Accessory Reproductive Glands: Seminal Vesicles
Enters the pelvic urethra at the same area of the vas deferens. Present in all domestic species except the cat an dog.
Accessory Reproductive Glands: Prostate Gland
Surrounds the urethra. Multiple ducts carry secretions into urethra. The only accessory reproductive gland in the dog , present in all domestic animal.
Accessory Reproductive Glands: Bulbourethral Glands
AKA-Cowper's Glands. Present in all domestic species except the dog. Ducts enter urethra near caudal border of pelvis. Secrete mucinous fluid just before ejaculation that clears and lubricates the urethra.
Penis: Male Breeding Organ
Composed of muscle, erectile tissue and connective tissue with the urethra down the center. Large blood supply and many sensory nerve endings. Three main parts of the penis- the roots, the body , and the glans.
Penis: Roots
Bands of connective tissue that attach penis to the brim of the pelvis.
Penis: Body
Two bundles of erectile tissue (corpus cavernosum urethrae that surrounds the urethra and corpus cavernosum penis which is dorsal to the urethra). Erectile tissue composed of fibrous connective tissue and blood filled sinuses. When sinuses engorge with blood they enlarge. The sinuses along with the connective tissue around the sinuses control the erection.
Penis: Glans
Distal end; numerous sensory nerve. Different in every species. Cats have spines.
Penis: Prepuce
Sheath of skin that encloses the penis when it is not erect. Inner portion is smooth, moist mucous membrane.
Canine Penis: Os Penis
Bone in the penis; urethra runs through groove on ventral surface bone. Raccoons, beavers, walruses. Fractures, urethral stones.
Canine Penis: Bulb of the Glans
Enlargement toward rear of the glans, made up of erectile tissue. Engorges with blood during breeding but doesn't reach full size after ejaculation. Remains clamped in place by contractions of muscles surrounding vagina and vulva male and female "tied together". Erection of the bulb subsides in 15-20 minutes, DO NOT PULL THEM APART
Sigmoid Flexure
S Shape of non-erect penis of the bull, ram, and boar. Higher proportion of connective tissue to erectile tissue than other species so penis doesn't enlarge as much. Erection results from straightening of the sigmoid flexures from internal pressure. Causes the penis to protrude from the prepuce for breeding via the retractor penis muscle. Stretches during an erection and relaxes when the erection subsides.
Reproductive Functions: Erection
Enlargement of stiffening of the penis that prepares it for breeding, results from a parasympathetic reflex by sexual stimuli. Often involves olfactory cues and behavioral changes that signal the male that the female is in heat. Arteries dilate and increase blood flow into penis. Veins are compressed against brim of the pelvis by contractions of muscles in roots of the penis causing less blood to leave the penis.
Reproductive Functions: Ejaculation
Reflex, expulsion of semen from the penis. 1. Semen moves from accessory reproductive glands into the pelvis portion of the urethra, Sphincter at the neck of the bladder contracts and closes preventing semen from entering the bladder. 2. Rhythmic contractions of the urethra pump the semen out into the female reproductive tract.