Reproduction in Humans I Flashcards
male reproductive system female reproductive system gametogenesis menstrual cycle journey of sperm in female reproductive tract
Seminiferous tubules: location + function
Location: Seminiferous tubules are tightly coiled tubules present within the testes
Function:
1. Produces sperm (development of sperm is called spermatogenesis)
2. FSH (Follicle stimulating hormone) from anterior pituitary gland promotes spermatogenesis
Leydig cells/Interstitial cells
Location + function
Location: Leydig cells/interstitial cells are present between the seminiferous tubules in the testes
Function:
1. They produce testosterone (Male sex hormone)
2. Testosterone promotes sperm development
3. Luteinizing hormone (LH) from anterior pituitary gland promotes production of testosterone by interstitial cells
What can lead to reduced quality and number of sperms produced?
Consumption of alcohol, body building steroids and smoking decreases levels of testosterone leading to reduced quality and number of sperms.
Sertoli cells/Nurse cells
- Provide nutrition to developing spermatids
- Sertoli cells form blood testis barrier
Acrosome of sperm
- It is the cap on the head of the sperm
- Contains Hyaluronidase enzyme for penetration of the egg
Head of sperm
Contains 23 chromosomes from the father
Mid-piece of sperm
- Contains mitochondrion
- produces ATP (energy) for swimming/motility
Tail of sperm
- Flagellum used for swimming/motility
- Whiplash movement
Spermatogenesis
The formation of male gametes (Spermatozoa) in the testis is called spermatogenesis
Spermiogenesis
The transformation of non-motile, circular spermatids to motile, elongated sperms is called spermiogenesis
Spermiation
The sperm heads embedded in the Sertoli cells get finally released from the seminiferous tubule. This release is called Spermiation.
Hormones required for spermatogenesis
GnRH (Gonadotropin Releasing Hormone):
secreted by: Hypothalamus
stimulates:
* anterior pituitary gland
FSH (Follicle Stimulating Hormone):
secreted by: pituitary gland
stimulates: process of spermatogenesis
LH (Luteinizing Hormone):
secreted by: pituitary gland
stimulates: secretion of Testosterone by Leydig cells which stimulates Spermatogenesis
GnRH—> FSH—> ( ) and LH —> (Testosterone) ===> SPERMATOGENESIS
GRW the testes hang in the scrotal cavity
The temperature in the scrotal cavity is comparatively lower than the abdomen (2-3 degrees Celsius lower) which provides a conducive environment for the production of sperm
Spermatogenesis- order + ploidy
- Primary germ cell (2n)
- Spermatogonia (2n)
- Spermatocyte - Primary spermatocyte (2n) and Secondary spermatocyte (n)
- Spermatid (n)
- Spermatozoa/Sperm (n)
Ovaries
- Produce eggs (ova)
- Produce hormones- estrogen and progesterone (female sex hormones)
Endometrium- functions + location
Location: The inner lining of the uterus is called the endometrium
Functions:
* It is the vascular site for the implantation of the embryo
* It helps form the placenta
* Endometrium lining is shed during menstrual cycle
Cervix: location and function
Location: Opening between uterus and vagina
Function: Produces mucus to help guide sperm towards the uterus
Oogenesis
The formation of ova in the ovary from primordial germinal cells is said to be oogenesis
Ovulation
Release of egg/ovum (usually once a month) is called ovulation
Menarche
The onset of the first menstrual cycle in a girl (avg age- 11-14 years) is called menarche
Menopause
In women, around the avg age of 50 years where hormonal changes bring about the end of ovulation and the menstrual cycle is termed as menopause.
When does meiosis 1 of oogenesis begin?
- Meiosis 1 of the primary oocyte begins during foetal development.
- The primary oocyte remains arrested in Prophase 1 of Meiosis 1 until puberty.
Oogenesis: after puberty
- After puberty, the primary oocyte completes meiosis 1
- It produces a secondary oocyte and a polar body which may or may not divide again
- Secondary oocyte begins meiosis 2
- Secondary oocyte is ovulated
Oogenesis: After fertilisation
- After fertilisation, meiosis 2 continues
- Oocyte splits into an ovum and second polar body
- The nuclei of the sperm cell and the ovum unite, forming a diploid zygote
Oogenesis: order + ploidy
- Primary germ cell (2n)
- Oogonium (2n)
- Primary oocyte (2n)
- Secondary oocyte (n) and first polar body (n) (degenerates)
- Ovum (n) and second polar body (n) (degenerates)
- After fertilisation- Zygote (2n)
How many spermatazoa/ova are formed after two meiotic divisions?
4 spermatozoa
1 ovum
Menstrual cycle
The rhythmic series of changes in the sex organs throughout the reproductive life of a female primate from menarche to menopause is called menstrual cycle.
Name the phases of the menstrual cycle
- Menstrual phase/Bleeding phase/Menses
- Proliferative phase/Follicular phase
- Ovulatory phase
- Secretory phase
Avg length of menstrual cycle
28 days
Avg length of phases of menstrual cycle
- Menstrual phase/Bleeding phase/Menses: 3 to 5 days
- Proliferative phase/Follicular phase: 6th to 13th day
- Ovulatory phase: 14th day
- Secretory phase: 15th to 28th day
FSH- full form + secreted by + when it is secreted most + function
FSH- Follicle stimulating hormone
Secreted by the pituitary gland
High at the initial stage of menstrual cycle (1-12 days)
Function:
1. Helps in growth and maturation of the Graafian follicle
2. Stimulates Estrogen secretion by the ovary
LH- full form + secreted by + when it is secreted most + function
LH- Luteinizing hormone
Secreted by the pituitary gland
High during ovulation (14th day)
Function:
1. Development of Corpus luteum which produces progesterone
2. Brings about ovulation
Estrogen- secreted by + function
Secreted by the ovary
Functions:
1. Repairs the endometrium after menstruation
2. Thickens endometrium anticipating implantation
Progesterone- secreted by + function
Secreted by the ovary
Functions:
1. Inhibits FSH production and therefore stops further follicle formation
2. Prepares the endometrium for implantation
GnRH- full form + secreted by + function
Gonadotropin releasing hormone
Secreted by the hypothalamus
Function: It controls the release of FSH and LH from the pituitary
hCG- full form + produced where + what
hCG- Human Chorionic Gonadotropin
Produced by the embryonic chorion in the placenta 6 days after fertilisation
Test to confirm pregnancy
How does the sperm enter the female reproductive tract?
The entry of sperm into the female reproductive tract is through the process of sexual intercouse (Coitus)
How much semen containing how many sperms is discharged into the vagina during coitus?
1.5 to 5 ml of semen containing about 200-500 million sperms
What is the first barrier?
The optimum pH for sperm viability is 7.0-8.5 (slightly alkaline) while the vaginal pH is 3.5-4.0 (acidic)
This is toxic to sperms and is the first barrier (sperms with less viability die)
What happens after ejaculation?
- The seminal fluid and cervical mucus act as buffers
- Vaginal pH rises to 7.0 for about an hour after ejaculation
- THe mucus plug at the cervix opens up due to influence of estrogen, facilitating the entry of sperms into the uterus
What is the second barrier?
The less motile and defective sperms are eliminated by the cervical mucus
How many spermatozoa enter the uterus?
around a thousand
What is the third barrier?
The spermatozoa move up the uterus, guided by the muscular contractions of the uterus.
The resistance of the endometrium leads to further reduction in sperms. This is the third barrier (Spermatozoa lose motility)
What is the fourth barrier?
- The spermatozoa swim through the utero-tubal junction to reach the fallopian tube
- The viscous fluid of the fallopian tubes contain Ca2+ ions that increase motility of the sperm.
- Some sperms get caught in the cilia of the fallopian tube
- This is the fourth barrier (sperms die)
Where are the sperms stored after crossing the fourth barrier?
In the utero-tubal junction, the sperms are stored in a reservoir in a sterile environment.
What happens to the sperm at the time of ovulation?
- At the time of ovulation, the sperm gets capacitated and hyper activated
- Capacitation is the final maturation of the sperm in the female reproductive system
What happens to the egg released during ovulation
It is taken up by the fimbriae of the fallopian tube
How long can the sperm and egg survive?
After ejaculation, the sperm can survive ~72 hours in the female body
The egg can survive only 12-18 hours
Where does fertilization occur?
In the ampullary-isthmic junction of the fallopian tube
How does fertilization take place?
After the spermatozoa get capacitated-
1. By whiplash movement of the tail, sperm swims towards the ovum
2. The egg is taken up by fimbriae of the fallopian tube
3. Sperm can survive ~72 hrs and egg 12-18 hrs in the female body
4. The membrane of the head region is lost which helps in the release of Hyaluronidase enzyme
5. Corona radiata contains follicle cells that are glued together by hyaluronic acid
6. Hyaluronidase acts on hyaluronic acid facilitating the entry of sperm to Zona pellucida (transparent region)
7. Ovum release the chemical Fertilizin, complementary to Antifertilizin in sperm (FINAL SELECTIVE BARRIER)
Implantation
THe attachment of embryo the the endometrium of the uterus is termed as implantation
Duration between ferilization and implanation
8-9 days
