Fertilization After breeding, the sperm and egg unite to form a zygote. After the nuclei have fused the zygote becomes an embryo. Embryos do not have any anatomical form.

Fertilization Fetus is the potential offspring still within the uterus. Conceptus is the product of conception which includes: Embryo Membranes placenta

Development of zygote After fusion of nuclei, the zygote undergoes a series of mitotic division. The first division creates a two celled embryo. These cells are called blastomeres. Each blastomere undergoes divisions yielding 4, 8, and 16 daughter cells. Twins are derived from blastomeres of a 2-celled embryo that divide independently.

Development When a solid ball of cells is formed and blastomeres can’t be counted, the embryo is called a morula. During this stage, fluid fills the cell and creates a cavity called a blastocoele. When a distinct cavity is recognized, the embryo is called a blastocyst. After growing, the blastocyst starts to crack the membrane and now becomes a free-floating embryo in the uterus.

Development

Development As the hatched blastocyst continues to grow, it forms three different layers known as the endoderm, ectoderm, and mesoderm. Ectoderm CNS Sense organs Mammary glands Sweat glands Skin Hair Mesoderm Circulatory Skeletal Muscle Reproductive tracts Kidneys Urinary ducts Endoderm » Digestive » Liver » Lungs » Pancreas » Thyroid gland » Other glands

Break time

Placenta The placenta is a transient organ of metabolic interchange between mother and offspring. Also produces a variety of hormones. Placentas have 4 different membranes: Allantois Yolk sac Amnion Chorion

Placental Membranes Yolk Sack In birds to nourish embryo In mammal a source of blood cells and primordial germ cells Amnion Non-vascular, fluid filled Fluid produced by fetus Protective cushion Ruptures at birth

Placental Membranes Allantois Blood vessels Fuses with chorion Brings blood vessels to chorion Chorion Outermost membrane Attachment to mother

Chorion Allantochorion (Chorioallantois) Allantois Cavity Cotyledon Amniotic Cavity Amnion Yolk Sack Yolk Sack

Placenta The functional unit of the placenta is the chorionic villus. Placentas are classified according to their chorionic villi. The four classifications are: Diffuse Zonary Discoid Cotyledonary

Placenta Diffuse: Pig & horse Characterized by having uniform distribution of the villi covering the surface. Microcotyledons are the functional interface between mother and offspring

Placenta Zonary: Dogs & cats A prominent region of exchange that forms a zone around the middle of the conceptus.

Placenta Discoid: Rodents & primates Characterized by having one or two distinct adjacent discs. These discs interface with the endometrium and provide nutrient and metabolic waste exchange.

Art

Placenta Cotyledonary Ruminants (cows, sheep, goats, deer, etc.) Characterized by having numerous, button-like structures called cotyledons. Cotyledons are the placental unit for blood vessels and connective tissue. A placentome consists of a fetal cotyledon and a maternal cotyledon.

Re-cap

Break Stand up and shake off your hands

Parturition A complex cascade of events Triggered by the fetus Separated into three stages: 1. Initiation of contractions 2. expulsion of fetus 3. expulsion of membranes

Stage 1 “Labor” Initiated by fetus Fetus becomes stressed due to lack of Nutrients Oxygen Space This stress leads to a series of hormone secretions initiating contractions and dialation.

Stage 1 comparison Cow – 2 to 6 hours Dog 6 to 12 hours Horse – 1 to 4 hours Alpaca – 2 to 6 hours Human – 8+ hours

Stage 2 Expulsion of the fetus As the hormones increase so do the contractions As the contractions increase, the feet and head of the fetus put pressure on the membranes causing them to rupture. As the fetus enters the birth canal, they become hypoxic causing stronger contractions. Positive feedback loop

Stage 2 comparison Cow – 30 to 60 min Dog – 6 hours Horse – 12 to 30 min Alpaca – 5 to 90 min Human – 2 hours

Stage 3 Membrane expulsion In most species, stage three quickly follows stage 2. Easy process Retained placenta Can cause disease, need to be removed manually

Stage 3 comparison Cow – 6 to 12 hours Dog – 15 minutes Horse – 1 hour Alpaca – 45 to 180 min Human – 1 hour or less

Dystocia Difficult birth Difficulties usually occur in the second stage due to the fetus not positioned correctly. Other causes Size of fetus Improper rotation (head comes first) multiple births

Puerperium The period after birth in which the reproductive tract returns to non-pregnant conditions. 4 events of puerperium Myometrial contractions Endometrial repair Resumption of ovarian function Elimination of bacteria

Lactation Lactation ensures that the newborn does not have to obtain food on its own. Everything that the mother eats is broken down into the nutrients that the offspring receives. The newborn receives all these nutrients in the form of milk. The newborn must receive milk, colostrum, right after birth or it will die. Colostrum contains antibodies and growth hormones

Colostrum vs. milk

The Mammary Gland Exocrine gland; common to all mammals; Mammary glands are sophisticated sweat glands Function: nourish the neonate - Food source: fat, protein, sugar (CHO), vitamins, minerals, water - Protection: immunoglobulins

Growth of the mammary glands Between birth and puberty The mammary gland experiences isometric growth Between puberty and pregnancy Grows allometrically (faster than the body) 4 hormones responsible for growth Progesterone, estrogen, prolactin, growth hormone During pregnancy Alveoli begin to develop into lobules Placental lactogen is responsible for secreting milk

Anatomy

Anatomical differences- Inguinal 2 Canals per teat Camel and cow

Anatomical Differences- Inguinal 1 Canal per teat Sheep, goat

Anatomical Differences- Inguinal 2-3 ducts per teat Pig, horse

Anatomical Differences- Inguinal 5-6 ducts per teat Dog, cat, rodents, rabbits

Anatomical Differences - thoracic 8-10 ducts per teat Primates, elephants

Milk ejection Transfers the milk from the alveoli to the ducts Milk ejection is a neuroendocrine reflex requiring Sensory activation (stimulation, auditory) Neural activation of hypothalamus Oxytocin release Contraction of myoepithelial cells Transfer of milk into ducts

Cool facts Kangaroos can nurse from two different teats; one joey can be 6 months of age another can be just born. The mother can produce two different kinds of milk. The alpine black salamander is pregnant for 3 years. In sea horses,the male is responsible for giving birth. The female lays her eggs into his pouch to grow. “Caesarian” came from Julius Caesar who was said to be born by an incision in the abdomen and uterine wall of his mother.