Yr 11 - Human Reproduction

Testes

Structure:

• There are 2 testes

• Divided into lobules

Function:

• Where spermatozoa are produced

Scrotum

Structure:

• Production of sperm requires a temperature of 2°C lower that body temp, so the scrotum holds the testes outside of the body.

• Skin covered pouch

Function:

• Holds and supports the testes

• Contraction of smooth muscle fibers in walls of scrotum can pull testes closer to the body is temp drops too low, the relaxes if temp too high

Seminiferous tubules

Structure:

• Testes are divided into lobules, each containing ST.

• All ST eventually join at a duct that enters the epididymis.

Function:

• Lined with cells that produce male gamete (spermatogonia)

• Between tubules are interstitial cells that secrete testosterone

Epididymis

Structure:

• highly coiled 6m tube

Function:

• stored sperm for 1 month while they mature.

Vas deferens

Structure:

• Runs from epididymis into abdominal cavity, loops over top of bladder.

• Under the bladder, two vas deferens join the urethra.

Function:

• during ejaculation, VD carries sperm away from epididymis to leave the testes

Urethra

Structure:

• Passage from bladder and vas deferens and through the penis

Function:

• transports both urine and sperm out of the body

Penis

Structure:

• Composed of erectile tissue

Function:

• Organ for passing urine and sperm

• Becomes erect so it can successfully be introduced into the vagina

Erectile tissue

Structure:

• Connective tissue that has a large number of sponge-like spaces

Function:

• spaces fill with blood causing the penis to enlarge, stiffen and become

Foreskin

Structure:

• Covers the head of the penis

Function:

• Protection of the head of the penis

Bulbo-urethral gland

Structure:

• X2

• small yellow glands ~ the size of a pea

Function:

• Secretes clear mucus that acts as a lubricant and precedes the emission of semen

Seminal vesicles

Structure:

• X2

• Pouch-like organ

Function:

• secretes thick fluid rich in sugar

• makes about 60% of the volume of semen

Prostate gland

Structure:

• X1

• Donut shaped gland

Function:

• Secreted a thin, milky, alkaline fluid

Testes gland

Composition:

• Spermatozoa

Function:

• To fuse with an ovum making a zygote

Seminal Vesicles Glands

Composition:

• Thick sugar rich fluid

Function:

• Nourishes sperm

Prostate Gland

Composition:

• Thin milky alkaline fluid

Function:

• Neutralise the acidic nature of the vagina.

Bulbourethral Glands

Composition:

• Clear mucus

Function:

• To lubricate the head of the penis.

Ovary

Structure:

• X2

• almond-shaped gland ~3cm in length.

• Supported in abdominal cavity by ligaments

Function:

• Location of ova production

Fimbriae

Structure:

• fingerlike projections from the fallopian tube

Function:

• guide the ova into the tube from ovary.

Fallopian tube (oviduct)

Structure:

• Walls composed of smooth muscle which contract

• Lined with cilia

• Both move ova along

Function:

• carries ova from ovary to uterus.

Uterus

Structure:

• a single, hollow, pear-shaped organ

• Behind bladder and in front of the rectum.

• Held in position by ligaments.

Function:

• Protects and nourishes developing foetus

Endometrium

Structure:

• Wall of uterus made of smooth muscle lined with a mucous membrane

Function:

• site of implantation of blastocyte

Cervix

Structure:

• neck of uterus

• composed of smooth muscle

Function:

• control the passage of sperm/menstrual fluid.

Vagina

Structure:

• 10cm canal leading outside body.

• Muscular wall lined with mucous membranes

Function:

• capable of stretching to form birth canal during childbirth.

• Receives penis during intercourse.

Clitoris

Structure:

• contain erectile tissue, blood vessels and nerves

Function:

• engorges when stimulated

Labia Majora

Structure:

• fleshy folds of skin made up of fat and fibrous tissue

• Surround urethra and vagina opening

Function:

• contain glands that produce oily secretion.

Labia Minora

Structure:

• Between labia majora

• Pinkish

• Lack fat and pubic hair

Function:

• Surround urethra and vagina opening

Urethra

Structure:

• Tube running from bladder to outside the body

Function:

• Transports urine out of the body

Define gametogenesis

The formation and development of the gametes.

State where spermatogenesis occurs and what is produced at the end of this process

Where it occurs: In the seminiferous tubules of the testes

What is produced: The formation and development of the spermatozoa.

Identify the type of cell division associated with spermatogenesis

Meiosis

Spermatogonium

• Diploid

• Undergoes mitosis

• 1

Primary spermatocyte

• Diploid

• Enlarges

• Undergoes meiosis 1

• 2

Secondary spermatocyte

• Haploid

• Undergoes meiosis 2

• 3

Spermatid

• Haploid

• Mature into spermatozoa

• 4

Spermatozoa

• Haploid

• Stored in epididymis

• 5

State where oogenesis occurs and what is produced at the end of this process.

Where it occurs: Occurs in the ovaries

What is produced: Produces 1 x haploid ovum and 3 x polar bodies

Identify the type of cell division associated with oogenesis

Meiosis

Oogonium

• Diploid

• Mitosis / undergoes growth

• 1

Primary oocyte

• Diploid

• Starts meiosis I, but pauses at birth Meiosis I is completed at puberty once a month

• 2

Secondary oocyte

• haploid

• Starts meiosis II, but pauses at ovulation If fertilised, completes meiosis II

• 3

Polar body

• haploid

• Contains minimal cytoplasm Gets reabsorbed

• 4

Ovum

• haploid

• Fuses with spermatozoa to create a zygote

What is an endocrine gland?

An endocrine gland is a gland that produces and releases hormones.

What is a hormone?

Chemical messengers that play an important role in the development and maintenance of body structures

Follicle stimulating hormone

Released from: pituitary gland

Target organ/cell: M: seminiferous tubules in testes F: ovaries

Effect of hormone: M: begin production of sperm F: Stimulates the development and maturation of follicles

Luteinising hormone

Released from: pituitary gland

Target organ/cell: M: testes F: follicle in ovaries

Effect of hormone: M: stimulate secretion of testosterone F:Promotes final maturation of follicle in ovary, ovulation and formation of the corpus luteum

Oestrogen

Released from: the ovarian follicle and corpus luteum

Target organ/cell: Various

Effect of hormone: Development of female reproductive system and secondary sexual characteristics (breast enlargement, broadening of hips, pubic hair)

Progesterone

Released from: corpus luteum

Target organ/cell: uterus • placenta • breast tissue

Effect of hormone: to maintain the endometrium, to develop and maintain the placenta if fertilisation occurs, to develop milk-secreting glands

Human Chorionic Gonadotropin

Released from: placenta

Target organ/cell: corpus luteum

Effect of hormone: maintain corpus luteum in early stages of pregnancy

Prolactin

Released from: pituitary gland

Target organ/cell: breast tissue

Effect of hormone: Preparation and maintenance of milk production

Oxytocin

Released from: pituitary gland

Target organ/cell: smooth muscle of uterine walls

Effect of hormone: Contractions during child birth

Testosterone

Released from: Interstitial cells in testes

Target organ/cell: Testes • Various

Effect of hormone: Development of mature spermatozoa • Maintenance of male reproductive organs and sex drive. At puberty it also influences development of secondary sexual characteristics (voice change, pubic hair, facial hair)

Identify which hormones the ovarian cycle is regulated by.

Regulated by FSH and LH

Follicular phase : Day 1-12

FSH and LH slowly increase, promoting growth and maturation of follicles through the following steps:

1) Cells forming wall of primary follicle enlarge and divide, creating a layer of cells around developing primary oocyte

2) Secretions from cells (of primary follicle) create a fluid filled space that gradually forces the oocyte to the edge of the follicle. Now considered secondary follicle. Within the follicle, the primary oocyte completes meoisis-1 and then pauses on metaphase-2

3) Fluid continues to accumulate within follicle, continues to enlarge and moves towards surface of ovary

4) On reaching the surface, the oocyte produces a budge on the surface of the ovary. It is now called a mature follicle Note: As the follicle grows, it secretes oestrogen and a low level of progesterone

Ovulation: Day 13-14

• High oestrogen levels (secreted from the developing follicles) stimulate a spike in LH and FSH

• Surge in LH results in ovulation of most mature follicle (others breakdown)

• Ovulation: mature follicle bursts expelling secondary oocyte (paused in metaphase-2) into fallopian tube (then swept along by beating of cilia and smooth muscle contractions)

Luteal phase: Day 15-28

• Post ovulation, the ruptured follicle collapses and the blood within forms a clot. The clot is absorbed by the remaining follicle cells, which enlarge and change colour to a cream and forms the corpus luteum (yellow body)

• Corpus luteum secretes oestrogen and progesterone Remember: Progesterone prepares endometrium for implantation and inhibits release of FSH and LH (prevent other follicles developing)

If fertilisation does NOT occur:

• Corpus luteum begins to degenerate after 8-10 days into a fibrous mass of scar tissue called the corpus albicans (white body) which eventually disappears Another ovarian cycle begins as no progesterone or oestrogen is being released so FSH and LH begin to increase

If fertilisation DOES occur:

• Corpus luteum continues to develop and ovarian cycle ceases

• Corpus luteum is maintained by human chorionic gonadotrophin secreted from the placenta.

• Once the placenta is developed, corpus luteum degenerates slowly

State the importance of an erection occurring prior to sexual intercourse.

Enables penis to enlarge and become firm to be able to penetrate vagina for sperm to be deposited in the vagina

Describe what occurs during ejaculation.

Rhythmic contractions of the epididymis, the vas deferens, the seminal vesicles, prostate gland following sexual stimulation of the penis. Propels the content of the ducts and glands into the urethra and out of the body.

Define insemination.

When the male ejaculates and the sperm is released into the vagina of a female.

Millions of sperm are released into the vagina when the man ejaculates. Explain why so many are released when only one is required to fertilise an ovum.

Mortality rate of sperm is very high. Therefore this increases the chance of one sperm being able to survive and fertilise the egg.

passage of sperm post insemination.

Vagina —> cervix —> uterus —> fallopian tubes

Describe the corona radiata and zona pellucida and explain how sperm are able to reach the oocyte contained within.

Corona radiata is the outer layer consisting of follicle cells joined together by cementing materials (acid) and the zona pellucida (is a glycoprotein matrix) which is the plasma membrane of the oocyte. The sperm use the enzyme located in their head to break down the materials.

Describe the events that take place once the sperm has entered the oocyte.

When the plasma membrane of the sperm and the oocyte fuse the nucleus of the sperm enters the ovum. Which then causes a fertilisation membrane to form around the oocyte preventing the entry of any more sperm.

Define fertilisation.

Fertilisation occurs when two haploid gametes, a sperm and an ovum combine to form one diploid cell (the zygote).

Explain the difference between and ovum, a zygote and an embryo.

• Ovum- the mature oocyte (after secondary oocyte has completed meiosis 2)

• Zygote- structure that forms when the two pro-nuclei have fused to create a diploid cell.

• Embryo- following fertilisation to the end of the eight weeks of pregnancy.

Describe implantation and state its purpose.

The process of implantation is where the embryo sinks into the lining of the uterus. This allows the blastocyst to gain nourishments for growth and development by absorbing nutrients from the endometrium

What is cell differentiation and provide an example.

Cell differentiation is the process by which immature, unspecialized cells become specialized cells with distinct structures and functions to perform specific roles in an organism. Where given the right conditions, stem cells can differentiate into specialised cells of the body. Erythrocytes (red blood cells); Neurons (nerve cells); Skeletal muscle cells; Osteocytes (bone cells) etc

Describe the major difference between specialised cells (i.e. differentiated cells) and stem cells

Specialised cells have a particular structure and role (function) in the body, whereas stem cells do not.

Identify the three main characteristics of stem cells

• Not yet specialised ie. unspecialised

• Can differentiate to become specialised

• Undergo proliferation ie. multiply through repeated cell division