Reproduction

Question 1

What is the function of Sertoli cells in sperm transport, maturation and storage?

Answer 1

Spermatozoa released from Sertoli cells at spermiation, involving a complex process of removing excess cytoplasm. It is aided by oxytocin produced by Leydig cells, which enhances contractility of seminiferous tubules via action on myoid cells.

Question 2

What is the function of the rete testis in sperm transport, maturation and storage?

Answer 2

Spermatozoa look fully mature but are not fully motile and are carried along in the bulk flow of seminiferous tubular fluid to the rete testis.

Question 3

What is the function of the efferent ducts in transport, maturation and storage of sperm?

Answer 3

Efferent ducts transport spermatozoa from the rete testis to the epididymis. These ducts absorb 90% of seminiferous tubular fluid. This dramatically slows the rate of flow and concentrates the spermatozoa. So transport here occurs by tubular smooth muscle contraction and the action of cilia in the efferent duct epithelium. Fluid absorption is dependent on oestrogen produced by Sertoli cells.

Question 4

What is the function of the epididymis in the transport, maturation and storage or sperm?

Answer 4

Spermatozoa are matured as they are transported through the epididymis (a single, long, highly coiled tube). Maturation is dependent on DHT stimulating the epididymis. The blood-epididymis barrier protects the spermatozoa. In the epididymis, sperm acquire:

• Motility, so they can swim progressively.
• Fertilising capacity – middle and terminal segments of epididymis secrete products, like fructose and glycoproteins, which coat sperm.

Fluid absorption continues in the initial segment of the epididymis to further concentrate spermatozoa. Transport depends on epididymal contractions, enhanced by oxytocin. Time for transport varies but is typically 2-5 days.

Question 5

What is the function of the cauda of the epididymis in the transport, maturation and storage of sperm?

Answer 5

Cauda of epididymis is specialised for sperm storage and stores sperm for 3-13 days, depending on species and sexual activity.

Question 6

What is the extragonadal sperm reserve?

Answer 6

The spermatozoa stored in the ductus deferens and predominantly the cauda of the epididymis form what is known as the extragonadal sperm reserve. This is the store of fully mature sperm that can be ejaculated and provides some degree of control over the number of sperm in any one ejaculate. This enables males to decrease the number of spermatozoa ejaculated in repeated matings with the same female, but to increase the number of spermatozoa ejaculated when mating with a new female.

Question 7

What is the function of the ductus deferens in the transport, maturation and storage of sperm?

Answer 7

Ductus deferens transports spermatozoa to the urethra for ejaculation.

• Ligation of the ductus deferens in vasectomies does not disrupt the sperm production or damages the testicles.
• Build up of spermatozoa is prevented by phagocytosis by immune cells within the epididymis and leakage of spermatozoa through the epididymis wall.

Question 8

What is the composition of seminal fluid?

Answer 8

• Fructose, glucose or sorbitol – main energy source for swimming.
• Buffers – help to neutralise acidic pH pf vaginal fluid
• Proteins – largely unknown functions with considerable species variation, including enzymes and coagulants in some species, as well as motility factors.
• Citric acid – chelation of divalent cations
• Paracrine agents such as prostaglandins
• Potentially infectious agents

Question 9

What is the length of oestrus cycle, length of oestrus, ovulations and length of pregnancy of cows?

Answer 9

Oestrus cycle = 21 days, polyeostrus
Oestrus = 18 hours
Ovulation = 11 hours after end of oetsrus
Pregnancy = 282 days

Question 10

What is the length of oestrus cycle, length of oestrus, ovulations and length of pregnancy of ewes?

Answer 10

Oestrus cycle = 17 days, seasonal
Oestrus = 29 hours
Ovulation = near end of oestrus
Pregnancy = 148 days

Question 11

What is the length of oestrus cycle, length of oestrus, ovulations and length of pregnancy of sows?

Answer 11

Oestrus cycle = 21 days, polyoestrus
Oestrus = 48-72 hours
Ovulation = 35-45 hours after the start of oestrus
Pregnancy = 115 days

Question 12

What is the length of oestrus cycle, length of oestrus, ovulations and length of pregnancy of mares?

Answer 12

Oestrus cycle = 21 days, seasonal polypestrus
Oetsrus = 4-8 days
Ovulation = 1-2 days before end of oestrus
Pregnancy = 335 days

Question 13

What is the length of oestrus cycle, length of oestrus, ovulations and length of pregnancy of dogs?

Answer 13

Oestrus cycle = 6 months
Oestrus = 9 days
Ovulation = 4-24 days after start of oestrus
Pregnancy = 63 days

Question 14

What is the length of oestrus cycle, length of oestrus, ovulations and length of pregnancy of cats?

Answer 14

Oestrus cycle = 17 days
Oestrus = 9 days
Ovulation = induced
Pregnancy = 63 days

Question 15

Describe the oestrus cycle of the bitch.

Answer 15

• 20 days before proestrus, there is a rise in FSH that drives follicular growth. These follicles are destined to be ovulated.
• Proestrus is where the dog has bloody discharge, but is not receptive to the male in this period. There is an increase in oestrogen because the follicles are growing and secreting oestrogen.
• Oestrogen peaks just before the end of proestrus and stimulates the LH surge for ovulation 2-3 days later.
• In oestrus, blood discharge changes from blood coloured to straw coloured. In heat for 7-10 days. Corpus luteum forms and there is an increase of progesterone.
• Unusually long anoestrous

Question 16

What are induced ovulators?

Answer 16

Require an external stimulus to cause the LH surge. Copulation stimulates the mechanoreceptors in the cervix.

The action potentials then travel via the brainstem to the hypothalamus, which secretes GnRH which acts on the anterior pituitary gland, which responds with an LH surge causing ovulation.

Because sperm is already on it way, pregnancy is pretty much assured.

Question 17

Describe the hormonal changes in the queen.

Answer 17

• Repeated oestrus behaviour lasting 9 days each time
• Followed by 8 day period of proestrus

Only do through these two stages and will keep repeating them until pregnancy.

63 days pregnant and then lactation period before cycling again.

Question 18

Define puberty and sexual maturity.

Answer 18

Puberty – the start of an animal’s reproductive life. In the female, this is the beginning of the ovarian activity and the first time of ovulation.

Sexual maturity – the age at which female attains full reproductive capacity.

Question 19

What are the species differences in timings of onsets of puberty?

Answer 19

Cat = 8 (4-12) months
Cow = 11 (9-24) months 
Dog = 12 (6-24) months 
Goat = 7-8 months 
Horse = 18 (12-19) months
Pig = 6 (5-7) months 
Sheep = 7 (4-14) months

Question 20

State 4 factors affecting puberty.

Answer 20

Hormonal
Environmental
Genetic
Nutritional

Question 21

Describe the shift in sensitivity between prepubital period and puberty.

Answer 21

Minimal GnRH release, FSH and LH are low and minimal to no folliculogenesis in prepubital period.

Increased pulse frequency and amplitude GnRH, increase in FSH and LH release and folliculogenesis occurs in puberty.

There is negative feedback on the hypothalamus and sensitivity to oestrogen increases.

Question 22

Why does sensitivity to oestrogen increase from prepubital period to puberty?

Answer 22

• Kisspeptin neurones play an important role on the positive feedback system on the GnRH neurones.
• Upregulation of mRNA for kisspeptin receptors on GnRH neurones.
• Synaptic changes to kisspeptin and GnRH neurones, dendrites and spine.
• Increase in sensitivity of GnRH neurones to kisspeptin.

Question 23

How does nutrition affect the onset of puberty?

Answer 23

• Body weight affects the onset of puberty
• Inadequate nutrition can affect seasonal breeders, as pregnancy and lactation have huge metabolic costs
• Hypothalamus also detects change sin adipose tissue, insulin, leptin, ghrelin and glucose levels

Question 24

How do pheromones environmentally affect the onset of puberty?

Answer 24

Pheromone secretion generate potentials from nasal receptors travel to the hypothalamus, where they impact GnRH release.

Question 25

Describe pigs as an example of pheromonal affect on the onset of puberty.

Answer 25

• Pigs reach puberty at 32 weeks of age.
• But if we increase the number of pigs housed together, the pigs reach puberty at a much younger age at 28 weeks.
• If we house 3 female pigs with 1 male, puberty is reached at 24 weeks.
• If we have a large group of females nearby (not even housed) with 1 male, they will also reach puberty at 24 weeks.

Question 26

How does photoperiod environmentally affect the onset of puberty?

Answer 26

Photoperiod/season controls the occurrence of reproductive cycles. Relies on 3 components:

• Photoreceptor and clock to distinguish log day from short day
• Endocrine system to act as an effector
• Nervous system linking photoreceptors and the endocrine system. It is the retino-hypothalamic-pineal pathway that is responsible for this.

Question 27

Describe how melatonin affects seasonal physiology.

Answer 27

Pineal gland secretes melatonin in response to darkness. Short days will have resultant long duration of melatonin secretion and long days have a short duration of secretion of melatonin.

1. Light levels detected by retina.
2. Impulses to the superchiasmatic nucleus of the hypothalamus and the superior cervical ganglion.
3. Postganglionic sympathetic nerve fibres on to the pineal gland inhibit pineal cells, preventing the synthesis of melatonin.
4. At night, light reduces and so retinal firing and inhibition is reduced, so melatonin is released.
5. Melatonin stimulates the synthesis and release of GnRH from the hypothalamus, causing pulses of LH from the pituitary gland.
6. High frequency pulses lead to breeding activity and low frequency LH pulses lead to anoestrous and inactive gonads.

Question 28

How do cells and tissues grow and develop in the oocyte and follicle to ovulation?

Answer 28

1. Squamous granulosa cells around primordial follicle
2. Cuboidal granulosa cells around oocyte
3. These divide and become several layers thick
4. Theca externa contains blood vessels, not granulosa cells
5. Granulosa cells are the follicles stimulated by gonadotropins and begin to secrete follicular fluid that coalesces in between these cells in the early antral follicle.
6. These increase in size until these pickets of fluid merge to form the antrum.

Question 29

Identify the stages of development of ovarian follicles.

Answer 29

Primordial follicles
Pre-antral follicles
Antral follicles
Pre-ovulatory follicles
Rupture 
Corpus luteum 
Corpus Albicans

Question 30

Define follicular atresia.

Answer 30

There are many signs of follicular degeneration. A few examples of atretic follicles are labelled on the virtual microscope. The final structure that remains in the ovary is the remnant of the zone pellucida, which is red.

First 4 stages of ovary development can undergo follicular atresia.

Question 31

Describe the structure of the foetal lungs.

Answer 31

The fetal lungs are unexpanded and filled with fluid that is produced by the type 2 alveolar cells via transcellular transport of Na+ and Cl-.

During the latter stages of gestation, activity of the respiratory muscles establish the movements that will be required during breathing after birth.

Question 32

Describe how the foetal lungs change at birth.

Answer 32

At birth, the release of adrenaline and glucocorticoids, coupled with the high oxygen levels after the first breath change the physiology of type 2 alveolar cells, which now actively reabsorb excess fluid into bloodstream and lymph, via expression of an ENaC sodium channel.

Question 33

What is the function of pulmonary surfactant and what produces it?

Answer 33

Type 2 alveolar cells.

• To decrease surface tension and therefore the wall tension within the lung alveoli. Without this decrease of surface tension, the force required to inflate the alveoli would be too great and the surface tension would collapse the lungs.
• To equalize the inflation of the alveoli, a consequence of La Place’s law which states that the pressure in a vessel is proportional to the tension in the wall of the vessel and inversely proportional to the radius of the vessel.

Question 34

Describe alveoli without surfactant.

Answer 34

The smaller radius alveolus has a higher gas pressure than the larger alveolus. This will cause air flow down the pressure gradient, from the small alveolus to the large alveolus, leading to collapse of the smaller alveolus and expansion of the larger alveolus. This inequality of expansion would be a serious limit on gas exchange in the lung.

Question 35

Describe alveoli with surfactant.

Answer 35

Fluid layer in the alveolus exists in a thicker layer in the smaller alveolus, which reduces the surface tension more in the smaller alveolus than the larger one. This equalizes the pressure between the alveoli and enables them to inflate more evenly promoting alveolar stability.

Question 36

What is the major mechanism that expels fluid from the lungs in the first breath?

Answer 36

The forceful first breath that draws fluid down into the expanding lungs where it is actively reabsorbed by the type 2 alveolar cells.

Question 37

Describe the pressures in the foetal circulation.

Answer 37

The high transmural pressures and low PAO2 in the lungs result in constriction of the pulmonary blood vessels, resulting in a high pulmonary vascular resistance and low blood flow.

In contrast, the systemic circulation is relatively low pressure, due to the low resistance of the placental circuit.

Question 38

Describe the mixing of blood in foetal circulation.

Answer 38

A high proportion of the oxygenated blood returning from the placenta bypasses the liver due to the ductus venosus and mixes with deoxygenated systemic venous blood in the caudal vena cava, reducing its O2 saturation.
This is directed by a structure known as the crista dividens to flow via the right atrium and the foramen ovale into the left atrium where the PO2 is decreased slightly by mixing with the small amount of deoxygenated blood returning from the pulmonary circulation.

Question 39

How does the foramen ovale close?

Answer 39

• The first breath decreases the transmural pressure on pulmonary blood vessels and causes vasodilation of pulmonary arterioles due to increased PAO2.
• Big drop in pulmonary vascular resistance and a substantial drop in pressure of the pulmonary artery, right ventricle and right atrium.
• Loss of the low resistance placental circulation as the umbilical blood vessels constrict and the umbilicus is torn.
• Increases total peripheral resistance of the systemic circulation and a rise in blood pressure in the aorta, left ventricle and left atrium.
• Decrease in peripheral vasodilation, which further increases systemic total peripheral resistance and systemic blood pressure.
• Higher pressure in the right atrium reverses the direction of blood flow through the foramen ovale preventing the right to left shunt of blood flow in the heart.
• This closes a flap over the foramen ovale, which becomes permanently sealed days to weeks later forming the fossa ovalis.

Question 40

How does the ductus arteriosus close?

Answer 40

• With the onset of breathing after birth, the pressure increase in the systemic circulation and decrease in the pulmonary circulation causes blood flow to reverse and oxygenated blood flows from the aorta through the ductus arteriosus into the pulmonary artery.
• High PO2 removes the tissue hypoxia and reduces the vasodilation of the ductus arteriosus.
• Fall in circulating PGE2-alpha following birth.
• Further vasoconstriction and flow is shut off.
• Ductus arteriosus is replaced by a band of fibrous tissue, the ligamentum arteriosum.

Question 41

Describe the species differences in closure of the ductus venosus.

Answer 41

• In some species, such as horses and pigs the ductus venosus closes at around the first third of gestation. In these species the oxygenated blood from the placenta will flow through the liver capillaries and mix with a small amount of venous blood from the hepatic sinusoids.
• But in other species, such as sheep, the ductus venosus is open throughout fetal life and shunts around 50% of the oxygenated blood from the placenta to the caudal vena cava bypassing the liver. Vasoconstriction of the ductus venosus in the postnatal period removes this short-circuit of the liver in these species.

Question 42

Describe the transmission of passive immunity in the foetus.

Answer 42

• The number of barriers between the fetal and maternal circulations is highest in the epitheliochorial placentas of horses, pigs and ruminants.
• The consequence of these barriers is that larger molecules, such as maternal antibodies cannot be transferred across the placenta from mother to fetus in these species.
• This means that horses, pigs and ruminants are born without any passive immunity.
• They therefore are totally reliant on postnatal transfer of maternal antibodies via the colostrum to prevent them from infectious diseases.

Question 43

Hoe does a ewe distinguish her lamb from others?

Answer 43

On the basis of its odour.

• The olfactory learning that enables selective lamb recognition occurs during a sensitive period of around 6 hours following parturition.
• This sensitive period is triggered by the vaginocervical somatosensory stimulation of giving birth and is associated with oxytocin release in the brain.

Question 44

How are bonding and rejection shown in ewes and lambs?

Answer 44

Selective bonding to her lamb is shown by increased incidence of receptive behaviours to her own lamb, which includes low-pitched bleats and acceptance of suckling, whereas rejection behaviours are shown towards alien lambs such as high-pitched bleats and butting.

Question 45

What is artificial vaginocervical stimulation used for?

Answer 45

If given VCS and then exposed to an alien lamb, the ewe will show increased acceptance and reduced rejection behaviours.

This is a useful procedure for trying to foster orphan or rejected lambs onto a maternal ewe.

Oxytocin and arginine vasopressin release in the brain are important for switching on maternal patterns of behaviour.