Chapter 24 Development

Fertilization and the Stages of Mitosis

What is embryonic Development? Do Now: What is embryonic Development?

(I) Embryonic Development In the early stages of development, the organism is called an embryo The process of embryonic development includes: 1. Cleavage 2. Gastrulation 3. Differentiation

(A) Cleavage Cleavage is a series of mitotic divisions where the cell increases in cell number but NOT in cell size Cleavage converts a single fertilized egg (zygote) into many cells

As cleavage continues, the cells form a hollow ball-type structure filled with fluid. At this point, the embryo is called a blastula

Stages of Development (Cleavage) Zygote 2 cells 4 cells 8 cells Morula Blastula Gastrula 2 layers 3 layer

Stages of Development (Cleavage)

(B) Gastrulation When the blastula reaches several hundred cells, gastrulation occurs In this stage, the cells on one side of the blastula push in and form a two-layered embryo called the gastrula

Gastrula The gastrula consists of 3 layers: a) endoderm – inner layer of cells b) mesoderm –middle layer of cells c) ectoderm - outer layer of cells

(C) Differentiation Differentiation- series of changes that transform the unspecialized embryonic cells into specialized cells, tissues and organs

Ectoderm Mesoderm Endoderm It is the three germ layers that give rise to all the tissues and organs of an animal Ectoderm Mesoderm Endoderm Nervous system Digestive System lining of mouth, nostrils, and anus epidermis of skin, sweat glands, hair, and nails bones and muscles blood and blood vessels reproductive and excretory system dermis layer of skin lining of digestive tract lining of trachea, bronchi, and lungs liver, pancreas thyroid, parathyroid urinary bladder

(C) Growth and Differentiation Differentiation- series of changes that transform the unspecialized embryonic cells into specialized cells, tissues and organs Growth- mot only are the number of cells increasing, but the size of the cells are increasing as well, and the embryo as a whole starts to develop

Farmer Andy

Two types of Development What are the 2 major types of development? Provide organisms that represent each.

Two types of Development External Development Fish, amphibians, reptiles, birds Internal Development Mammals and their is a Lack of Development !

Farmer Andy

External Development

External Development

External Development

(B) Internal Development Development occurs inside the female Three types: Placental mammals Marsupials Monotremes To be covered later

Egg Development What is the difference between these two eggs? http://chickscope.beckman.uiuc.edu/explore/embryology/day08/graphics/embryo_chick.mov

Chicken Reproductive System The ovaries appear like a bunch of grapes and in an adult will contain five to six developing egg yolks. The oviduct is divided into five regions: funnel or infundibulum, magnum where albumen is secreted, isthmus which secretes the shell membranes, uterus or shell gland, the vagina which connects to the cloaca. Chicken eggs are incubated about 21 days before hatching.

Chicken Reproductive System

Structure of Egg chorion- outer-most membrane, aids in gas exchange Consists of 4 membranes outside of the embryo chorion- outer-most membrane, aids in gas exchange allantois- exchange of O2 and CO2. Also a storage site for wastes amnion- sac containing amniotic fluid which surround the embryo, provides cushion and acts as a shock absorber yolk sac- source of food for the embryo. Blood vessels in the yolk sac transport food to the developing embryo

Structure of Egg chorion- outer-most membrane, aids in gas exchange Consists of 4 membranes outside of the embryo chorion- outer-most membrane, aids in gas exchange allantois- exchange of O2 and CO2. Also a storage site for wastes amnion- sac containing amniotic fluid which surround the embryo, provides cushion and acts as a shock absorber yolk sac- source of food for the embryo. Blood vessels in the yolk sac transport food to the developing embryo

Structure of Egg chorion- outer-most membrane, aids in gas exchange Consists of 4 membranes outside of the embryo chorion- outer-most membrane, aids in gas exchange allantois- exchange of O2 and CO2. Also a storage site for wastes amnion- sac containing amniotic fluid which surround the embryo, provides cushion and acts as a shock absorber yolk sac- source of food for the embryo. Blood vessels in the yolk sac transport food to the developing embryo Embryo

“Chicken Egg” germinal disc yolk chalaza shell inner shell membrane outer shell membrane air cell yolk membranes outer layer of thin albumen dense albumen inner layer of thin albumen chalaziferous layer “Chicken Egg”

Fertilization                                                                  In the infertile egg, on the left, the nucleus is merely a light spot on the yolk. The egg on the right is fertilized. In the fertilized egg the ovum has fused with a sperm to begin forming an embryo. By the time the fertilized egg is laid, many cells are divided on the surface of the yolk and formed a blastoderm. Can you see the difference between the nucleus of the infertile egg and the blastoderm of the fertilized egg? Both are indicated by the blue arrow.

Day 1                                                                  After one day in the incubator, the small white spot seen in the fertilized egg above has grown to the size of a nickel or a quarter.

Day 2 By 24 hours, pockets of blood cells and developing blood vessels, called blood islands, begin to appear on the surface of the yolk along the outer edges of the area opaca. These are called the vitelline vessels. At the same time, the heart and vessels within the chick embryo have begun to develop.                                                               

Day 3 The embryo is the question mark shape in the center of the image. It has grown considerably since yesterday and the anterior half of its body is curved even more. The heart, located inside the anterior curve of the body is much larger and more developed than in yesterday's photograph.                                                               

At four days, nearly the entire body of the embryo has risen off the yolk and turned to lay on its left side. The upper portion of the embryo is even more curved and the tail is also beginning to curve. The heart is the dark red area within the upper curve of the embryo. Just a fraction of an inch from the heart, the eye is visible. The large node just above and to the right of the eye is a portion of the brain. Day 4                                                                 

Day 5                                                                    Yolk Eye of embryo Albumen

Day 6                                                           Yolk Air space Eye of embryo Blood vessels

Day 7 A row of feather germs appears on the tail. The sclera of the eye begins to form. Feather papillae appear on the thigh. The leg bends at the knee. Day 7                                                                

Day 8 http://lancaster.unl.edu/4h/Embryology/Embryo.htm

Day 9

Welcome into the World

Hello World

I feel so naked

Hatching takes a lot out of You

1 hour

1 hour

20 Hours Old and they sleep like teenagers

22 hours

Left-Overs aren't always good

Do Now 4/28 What are the four membranes found in the adaptation for external development??

(B) Internal Development Development occurs inside the female Three types: Marsupials Monotremes Placental mammals

Marsupials Are mammals that do not have a placenta The embryo is born at a relatively premature stage, and completes its development externally in a pouch that contain mammary glands Examples are kangaroos, wombat, Tasmanian devil and opossum

Marsupials

Fainting: Adaptations that my not always work Marsupials Fainting: Adaptations that my not always work

Monotremes They are the only mammals that hatch their young from eggs. The echidna and the platypus

Monotremes

Placental Mammals These are animals, like humans, that contain a structure called the uterus where the embryo develops Within the uterus, a specialized structure called the placenta forms It is through the placenta that the exchange of nutrients, wastes, and respiratory gases between the embryo and the mother take place The umbilical cord, which contains blood vessels, attaches the embryo to the placenta

Placental Mammals

Placental Mammals

Umbilical cord

And now to Chapter 25, Sexual Reproduction and Development in humans