Human reproduction
description
Transcript of Human reproduction
Human reproduction
for A2 Biology
Part 1
DJH
Male reproductive system
Bladder
Pubic bone
Vas deferens
Erectile tissueUrethra
Penis
Glans
Prepuce
Seminal vesicle
Ejaculatory duct
Prostate gland
Cowper’s glandAnus
Epididymis
Testis
Scrotum
Spongy tissue
Female reproductive system
Pubic bone
Oviduct
OvaryFimbria
Uterus
Bladder
Urethra
Clitoris
Labium minorum
Labium majorumAnus
Vagina
Rectum
Cervix
Vertebra
Vaginal orifice Perineum
Male system memory check
Write down the name and one function
for as many of structures 1 to 19 as you
can.
Female system memory check
Write down the name and one function
for as many of structures 1 to 16 as you
can.
Quick test
Write down the name and one function of each of structures 1 – 11.
Quick test
Write down the name and one function of each of structures 1 – 14.
Gametogenesis
gametes are haploid in humans, n = 23 to produce gametes, diploid (2n) cells in
the ovary or testis must divide by meiosis
meiosis consists of two consecutive divisions: the first (reduction division) is the one that separates homologous chromosomes from each other
A reminder of mitosisIn mitosis,
• chromosomes are replicated in interphase (S phase of the cell cycle), to form sister chromatids joined at the centromere
• in prophase the replicated chromosomes condense by spiralisation, and become visible in the light microscope
• chromosomes line up on the equatorial plane, where spindle fibres attach to the centromeres (metaphase)
• the centromeres divide and the sister chromatids are pulled toward opposite poles (anaphase)
• the daughter chromosomes re-disperse, nuclear envelopes form around them, and cytokinesis occurs (telophase)
The animation shows mitosis in an animal cell where 2n = 4
Meiosis
At the beginning of prophase I chromosomes condense and become visible, as in mitosis.
As they continue to condense the homologous chromosomes pair up: this never happens in mitosis.
At this point the paired chromosomes are seen to consist of sister chromatids, joined at a centromere.
The pairs of chromosomes (each called a bivalent) move to the equatorial plane and attach to spindle fibres.
This is metaphase I
As the spindle fibres contract the homologous chromosomes are pulled apart.
This is anaphase IThis is late anaphase I, leading to telophase I
Telophase I usually leads straight into prophase II: the nuclear envelope may or may nor re-form.
This is late telophase I, leading to prophase II
Meiosis II is mechanically identical to mitosis: the separated chromosomes line up on the equatorial plane ...
This is metaphase II
... and the chromatids are separated by centromere division and spindle contraction
This is anaphase II
At telophase II four haploid and genetically different daughter cells have been produced
This is telophase II leading into interphase
This was the parent cell
… and this is how it divides
Meiosis: chiasmata and crossing over
During prophase I the chromatids of the paired homologous chromosomes become intricately entwined. At this stage they randomly break and re-join at points called chiasmata.
Chiasmata
When they separate at anaphase I, the homologous chromosomes now contain both maternal and paternal portions …
… leading to even greater genetic variation in the daughter cells (gametes).
Meiosis: how much have you understood?
These diagrams show four stages in meiosis prophase I.
1 What is the diploid number of this cell?
2 Put the diagrams into the correct order.
Meiosis: how much have you understood?
These diagrams show stages in meiosis.
1 Which division of meiosis is shown?
2 How would the diagrams differ if they showed the equivalent stages of division II?
Meiosis: how much have you understood?
These ten photographs show stages in meiosis in sea urchins. Put them into the correct order and identify each stage as precisely as you can. Each mouse click will move you on one step.
Done. If you got the sequence wrong, click the return arrow to try again. Otherwise, click the forward arrow to move on.
What happens next?
What happens next?
Outcomes of meiosis Four haploid daughter cells … which are genetically different
due to … independent assortment of
maternal and paternal chromosomes at metaphase/anaphase I …
and chiasma formation and crossing over during prophase I
SpermatogenesisSpermatogenesis takes place in the wall of the seminiferous tubules of the testes.
Spermatogenesis
A single seminiferous
tubule
Stages in spermatogenesis
1
2
3
4
5
Early spermatid
Spermatogonia
Late spermatids
Secondary spermatocytes
Primary spermatocytes undergoing meiosis 1
Sertoli cells
The cells undergoing spermatogenesis are embedded in and protected by Sertoli cells (nurse cells).
Mitosis
Meiosis I
Meiosis II
Spermiogenesis
Leydig cells (interstitial cells)
Leydig cells are found in the spaces between
seminiferous tubules: they
secrete testosterone
and other androgens.
Oogenesis
Objectives:* To be able to outline gametogenesis in the human male and female**To be able to explain the role of hormones in maintenance of the human menstrual cycle and link this to changes in the ovary and uterus during the Cycle
Oogenesis
Oogenesis starts in the foetal ovaries and continues from 5 to 25
weeks of foetal life.
At birth the ovaries contain about 3 000 000 primary oocytes, all
arrested in prophase of meiosis I.
At puberty, about 400 000 primary oocytes remain in the ovaries. In each menstrual cycle one or two of these are
stimulated to complete meiosis I: the division is unequal, forming a secondary oocyte and a small polar body.
The secondary oocyte starts meiosis II, but halts at metaphase. Meiosis II is completed only after fertilisation,
forming a second polar body and an ovum.
Comparison of spermatogenesis and oogenesis
Starts at puberty
Starts during foetal life: suspended until puberty
Continuous from puberty into old age
Four functional gametes produced from every
primary spermatocyte
Only one functional gamete produced from every primary oocyte
Re-starts at menarche: completed during menstrual cycles by only a small percentage of primary oocytes
Oogenesis in the ovary
In the foetal ovary diploid oogonia are produced by mitosis
Some of these divide by mitosis to produce primary oocytes, which start meiosis I
As they do so, some of the cells around them form a covering layer called a primordial follicle
During childhood some of the primordial follicles develop into primary follicles, in which the cells surrounding the oocyte form several layers called granulosa cells.
Cells around the granulosa cells form an additional layer around the follicle called the theca.
The granulosa cells themselves secrete a protective glycoprotein layer around the primary oocyte called the zona pellucida.
Oogenesis in the ovaryHormones secreted at puberty
stimulate primary follicles to develop into secondary
follicles: the primary oocyte (still stuck in prophase of
meiosis I) grows in size, and a fluid-filled space develops in
the follicle.
During each menstrual cycle one (usually) secondary follicle
is stimulated by the hormone FSH to develop into a
Graafian follicle: in the Graafian follicle the primary oocyte completes meiosis I, forming a small first polar
body and a secondary oocyte, which is expelled in
ovulation
The menstrual cyclePituitary secretes FSH; this triggers follicle development.Granulosa cells secrete oestrogens.
Oestrogens stimulate repair of endometrium …
… and secretion of LH by pituitary.
LH triggers ovulation …
… and development of remaining follicles cells into
corpus luteum.
Corpus luteum secretes progesterone …
…which stimulates vascularisation of endometrium and inhibits FSH
secretion
Corpus luteum degenerates, progesterone level falls;
endometrium breaks down, FSH secretion re-starts, a new cycle
begins
The ovarian cycle
Follicular phase: days 1-14
Secretory (luteal) phase:
days 14-28
Ovulation: around day 14
The uterine cycleIn the follicular (proliferative) phase the endometrium is repaired and thickened under the influence of FSH.In the secretory phase the endometrium becomes vascular and spongy under the influence of progesterone.
In the menstrual phase the endometrium breaks down as the corpus luteum degenerates and progesterone secretion fails.
How well have you understood the menstrual cycle?
What is breaking down here? Why?
What are these?What has caused this repair? Where was it made?
What has caused this development?What triggers this event?What is this? What does it produce?What has caused
this change? Where was it made?
What is this? How does it get here?
End of Part 1
Fertilisation, implantation, pregnancy, birth and lactation are covered in Part 2