Exam Preparation Notes

Ontogeny Recapitulates Phylogeny

• Definition: When you study embryonic development over and over, you will see more evidence that we have undergone evolutionary development.

• Example: Yolk Sac

  • Humans and birds both have a yolk sac structure during embryonic development.
  • Birds still use the yolk sac for nourishing the embryo, providing gas exchange, and contributing to the formation of structures like the umbilical cord and initial blood cells.
  • Humans don't use it anymore because the umbilical cord takes over the function of providing nutrients from the mother to the developing embryo.
  • The presence of the yolk sac in human embryos suggests that at some point in our evolutionary history, we needed this sac.

Embryonic Development and Evolutionary Evidence

• Studying embryonic development provides evidence of evolutionary development.

• Example: Yolk Sac

  • In the beginning, embryos used the yolk sac to provide nutrients.
  • Chickens still use it for nutrients.
  • Humans now use the umbilical cord instead.
  • The yolk sac in humans is now a vestigial structure.

Similarities in Embryos

• Observation: All embryos look the same initially.

• Interpretation: This suggests a common ancestor between all species.

• Divergence: During the evolutionary process, different embryos developed differently.

  • Some embryos kept a tail.
  • Some developed limbs.

Analogy to Monkey Evolution

• Just like the idea that humans may have evolved from monkeys, embryos start the same but evolve differently over time.

• Explanation:

  • We all started from the same point.
  • Some stayed as monkeys.
  • Some developed further.
  • Species evolved at different rates and directions.

Common Ancestry

• All embryos looking the same in the beginning indicates that we had embryos with the same genetics.

• Over time, evolution led to different features such as tails or limbs.

• The most common ancestors between all species must have looked the same.

Gastrulation

• Explanation: Explain gastrulation in the drawing and the description.

Human Embryos in Watery Environments

• Human embryos are suspended in water environments, similar to animals.

• This gives a lot of evidence for evolution as water environments were the original place that life began and developed supporting the idea that fish and humans were all in watery environments.

Blastocyst and Hormone Release

• The blastocyst releases a hormone called HCG (human chorionic gonadotropin).

• Function of HCG: Signals the ovaries to keep the corpus luteum alive, which keeps the endometrium intact.

• Importance of Corpus Luteum: It releases estrogen and progesterone.

• What happens without Corpus Luteum? Without these hormones, the stratum functionalis will shed.

• If a fertilized oocyte implants on the stratum functionalis and there is no corpus luteum, the stratum functionalis will shed, causing a natural version of an abortion.

• Successful Pregnancy: To have a successful pregnancy, you need the stratum functionalis, which relies on HCG produced by the blastocyst that communicates with the ovaries.

Corpus Luteum and Stratum Functionalis

• Blastocyst implants on the endometrium.

• Blastocyst releases HCG, signaling the ovaries to maintain the corpus luteum.

• Corpus luteum releases estrogen and progesterone.

• If corpus luteum stops releasing these hormones, the stratum functionalis will shed.

• If there is a fertilized oocyte implanted, this shedding results in a natural abortion.

Fertilization and Bleeding

• Bleeding or spotting can occur during pregnancy.

Organogenesis

• Definition: The development of organs.

• Timing: After two weeks of fertilization and for the next two months.

• Morphogenesis: The formation of the three-dimensional shape of the organs (e.g., bending and twisting of the heart).

• Differentiation: Specialization of cells.

• Stem Cells:

  • Totipotent stem cells: Can become anything.
  • Pluripotent stem cells: Can become a limited range of cells; have some DNA mapping but can still change what they become.
  • Unipotent stem cells: Can only become one type of cell.

Cell Decision-Making

• Chemical Gradient: A type of chemical that tells a stem cell what it needs to become, based on how much of that chemical it's exposed to.

Example:
*If a stem cell is close enough to a chemical, the chemical tells the stem cell what to become.

• Hormone Influence: How much of something also can affect a stem cell

Example:
*If a cell has some testosterone versus a cell that has a lot of testosterone, you might see a significant difference when it develops and specializes at that stem cell.

• Induction: When a group of cells communicate with another group of cells and then tells them where they are and what they need to develop into. This is done by physical contact. If you have two cells that are touching, then they can basically get, like, that information from that other cell.

Example:
*A chick embryo has teeth for a short time as descendants of dinosaurs.

*During development, at some point, the mesoderm stopped replicating the beak.

*If you want to take the mesoderm from a mouse and during the periods of where there are no more mesoderm in beak, you'll insert the mesoderm in, and then the mesoderm will turn to teeth. This is because of induction.

*There is a signal that the beak cells are capable of releasing, and this shows that they have retained genetic information to be able to do this.

Genetic Information

• If you give the cells in the yolk sac enough information and cells and genetic information that it can begin working again.

• This shows that organisms have retained genetic information that they are able to do this again.

Bile

• Definition: An emulsifier that breaks down big chunks of fat into smaller chunks of fat.

• Function: A form of chemical digestion.

• The pancreatic secretions and the biosecretions secretions come to this region, we have the sphincter called sphincter of Oddi, and then all of those secretions will go through the duodenum.

Production of Bile

• Bile is made in the liver from hemoglobin.

• Hemoglobin breaks down into bilirubin.

• Bilirubin then turns into bile.

• Hepatitis: Liver fails, preventing hemoglobin from converting to bilirubin, and bilirubin can't turn into bile.

• This can cause jaundice.

Types of Digestion

• Mechanical Digestion: Physically breaking down the food.

• Chemical Digestion: Using enzymes to break down food into smaller molecules.

Anatomy of the Liver Lobule

• The hepatic portal triad's three structures consist of vessels and ducts, hepatic arteries, hepatic portal vein, and then the bile ducts.

• The bile ducts will collect bile and send it over to the gallbladder or the small intestine.

*These will send blood over to the liver lobules then over to the central vein.

*The central vein is then gonna take blood, take all the blood that is sent through the liver lobule, and send the blood over to the inferior vena cava to become oxygenated.

*Hepatocytes are gonna be arranged in a way where we have space. It's called the hepatic sinusoid.

*Blood from the hepatic arteries and the hepatic portal vein are going to the hepatic sinusoid, and then hepatocytes will help with filtering. Whatever blood makes it to the central vein goes back to the heart.

*Hepatic arteries and the hepatic portal vein aren't blood vessels that send blood into the hepatic sinusoid. We're going to have to send them into the sinusoidal capillaries, also known as discontinued capillaries, and then we allow the red blood cells to escape from this region.

*We have the bile canaliculus, which is going to send bile that we have produced from the hepatic sinusoid, and we'll send it over to the bile ducts.

Kuppfer Cells

• Fixed macrophages that target old erythrocytes.

How Bile is Made in the Liver

• Old erythrocyte makes its way to the liver.

• Kupffer cell eats it and breaks it apart, forming bilirubin.

• Bilirubin is sent into a hepatocyte.

• Bile canaliculus takes the bile and sends it to the bile duct.